diff --git a/src/ContentMessages.ts b/src/ContentMessages.ts
index 85ca90067d..e05858bb16 100644
--- a/src/ContentMessages.ts
+++ b/src/ContentMessages.ts
@@ -89,7 +89,7 @@ async function loadImageElement(imageFile: File): Promise<{
 
     // check for hi-dpi PNGs and fudge display resolution as needed.
     // this is mainly needed for macOS screencaps
-    let parsePromise: Promise<boolean>;
+    let parsePromise = Promise.resolve(false);
     if (imageFile.type === "image/png") {
         // in practice macOS happens to order the chunks so they fall in
         // the first 0x1000 bytes (thanks to a massive ICC header).
@@ -101,7 +101,7 @@ async function loadImageElement(imageFile: File): Promise<{
             const chunks = extractPngChunks(buffer);
             for (const chunk of chunks) {
                 if (chunk.name === "pHYs") {
-                    if (chunk.data.byteLength !== PHYS_HIDPI.length) return;
+                    if (chunk.data.byteLength !== PHYS_HIDPI.length) return false;
                     return chunk.data.every((val, i) => val === PHYS_HIDPI[i]);
                 }
             }
@@ -199,10 +199,10 @@ function loadVideoElement(videoFile: File): Promise<HTMLVideoElement> {
                 reject(e);
             };
 
-            let dataUrl = ev.target.result as string;
+            let dataUrl = ev.target?.result as string;
             // Chrome chokes on quicktime but likes mp4, and `file.type` is
             // read only, so do this horrible hack to unbreak quicktime
-            if (dataUrl.startsWith("data:video/quicktime;")) {
+            if (dataUrl?.startsWith("data:video/quicktime;")) {
                 dataUrl = dataUrl.replace("data:video/quicktime;", "data:video/mp4;");
             }
 
@@ -258,7 +258,7 @@ function readFileAsArrayBuffer(file: File | Blob): Promise<ArrayBuffer> {
     return new Promise((resolve, reject) => {
         const reader = new FileReader();
         reader.onload = function (e): void {
-            resolve(e.target.result as ArrayBuffer);
+            resolve(e.target?.result as ArrayBuffer);
         };
         reader.onerror = function (e): void {
             reject(e);
@@ -329,7 +329,7 @@ export async function uploadFile(
 
 export default class ContentMessages {
     private inprogress: RoomUpload[] = [];
-    private mediaConfig: IMediaConfig = null;
+    private mediaConfig: IMediaConfig | null = null;
 
     public sendStickerContentToRoom(
         url: string,
@@ -377,8 +377,8 @@ export default class ContentMessages {
             modal.close();
         }
 
-        const tooBigFiles = [];
-        const okFiles = [];
+        const tooBigFiles: File[] = [];
+        const okFiles: File[] = [];
 
         for (const file of files) {
             if (this.isFileSizeAcceptable(file)) {
@@ -420,7 +420,14 @@ export default class ContentMessages {
             }
 
             promBefore = doMaybeLocalRoomAction(roomId, (actualRoomId) =>
-                this.sendContentToRoom(file, actualRoomId, relation, matrixClient, replyToEvent, loopPromiseBefore),
+                this.sendContentToRoom(
+                    file,
+                    actualRoomId,
+                    relation,
+                    matrixClient,
+                    replyToEvent ?? undefined,
+                    loopPromiseBefore,
+                ),
             );
         }
 
@@ -584,7 +591,7 @@ export default class ContentMessages {
     }
 
     private ensureMediaConfigFetched(matrixClient: MatrixClient): Promise<void> {
-        if (this.mediaConfig !== null) return;
+        if (this.mediaConfig !== null) return Promise.resolve();
 
         logger.log("[Media Config] Fetching");
         return matrixClient
diff --git a/src/DecryptionFailureTracker.ts b/src/DecryptionFailureTracker.ts
index 7329c665bc..256fe245ee 100644
--- a/src/DecryptionFailureTracker.ts
+++ b/src/DecryptionFailureTracker.ts
@@ -138,7 +138,7 @@ export class DecryptionFailureTracker {
             return;
         }
         if (err) {
-            this.addDecryptionFailure(new DecryptionFailure(e.getId(), err.code));
+            this.addDecryptionFailure(new DecryptionFailure(e.getId()!, err.code));
         } else {
             // Could be an event in the failures, remove it
             this.removeDecryptionFailuresForEvent(e);
@@ -146,7 +146,7 @@ export class DecryptionFailureTracker {
     }
 
     public addVisibleEvent(e: MatrixEvent): void {
-        const eventId = e.getId();
+        const eventId = e.getId()!;
 
         if (this.trackedEvents.has(eventId)) {
             return;
@@ -154,7 +154,7 @@ export class DecryptionFailureTracker {
 
         this.visibleEvents.add(eventId);
         if (this.failures.has(eventId) && !this.visibleFailures.has(eventId)) {
-            this.visibleFailures.set(eventId, this.failures.get(eventId));
+            this.visibleFailures.set(eventId, this.failures.get(eventId)!);
         }
     }
 
@@ -172,7 +172,7 @@ export class DecryptionFailureTracker {
     }
 
     public removeDecryptionFailuresForEvent(e: MatrixEvent): void {
-        const eventId = e.getId();
+        const eventId = e.getId()!;
         this.failures.delete(eventId);
         this.visibleFailures.delete(eventId);
     }
@@ -193,8 +193,8 @@ export class DecryptionFailureTracker {
      * Clear state and stop checking for and tracking failures.
      */
     public stop(): void {
-        clearInterval(this.checkInterval);
-        clearInterval(this.trackInterval);
+        if (this.checkInterval) clearInterval(this.checkInterval);
+        if (this.trackInterval) clearInterval(this.trackInterval);
 
         this.failures = new Map();
         this.visibleEvents = new Set();
diff --git a/src/DeviceListener.ts b/src/DeviceListener.ts
index eccfc1c0e3..039adc27cd 100644
--- a/src/DeviceListener.ts
+++ b/src/DeviceListener.ts
@@ -51,7 +51,7 @@ import { isBulkUnverifiedDeviceReminderSnoozed } from "./utils/device/snoozeBulk
 const KEY_BACKUP_POLL_INTERVAL = 5 * 60 * 1000;
 
 export default class DeviceListener {
-    private dispatcherRef: string;
+    private dispatcherRef: string | null;
     // device IDs for which the user has dismissed the verify toast ('Later')
     private dismissed = new Set<string>();
     // has the user dismissed any of the various nag toasts to setup encryption on this device?
@@ -152,7 +152,7 @@ export default class DeviceListener {
     private ensureDeviceIdsAtStartPopulated(): void {
         if (this.ourDeviceIdsAtStart === null) {
             const cli = MatrixClientPeg.get();
-            this.ourDeviceIdsAtStart = new Set(cli.getStoredDevicesForUser(cli.getUserId()).map((d) => d.deviceId));
+            this.ourDeviceIdsAtStart = new Set(cli.getStoredDevicesForUser(cli.getUserId()!).map((d) => d.deviceId));
         }
     }
 
@@ -162,7 +162,7 @@ export default class DeviceListener {
         // devicesAtStart list to the devices that we see after the fetch.
         if (initialFetch) return;
 
-        const myUserId = MatrixClientPeg.get().getUserId();
+        const myUserId = MatrixClientPeg.get().getUserId()!;
         if (users.includes(myUserId)) this.ensureDeviceIdsAtStartPopulated();
 
         // No need to do a recheck here: we just need to get a snapshot of our devices
@@ -170,7 +170,7 @@ export default class DeviceListener {
     };
 
     private onDevicesUpdated = (users: string[]): void => {
-        if (!users.includes(MatrixClientPeg.get().getUserId())) return;
+        if (!users.includes(MatrixClientPeg.get().getUserId()!)) return;
         this.recheck();
     };
 
@@ -225,7 +225,7 @@ export default class DeviceListener {
 
     // The server doesn't tell us when key backup is set up, so we poll
     // & cache the result
-    private async getKeyBackupInfo(): Promise<IKeyBackupInfo> {
+    private async getKeyBackupInfo(): Promise<IKeyBackupInfo | null> {
         const now = new Date().getTime();
         if (!this.keyBackupInfo || this.keyBackupFetchedAt < now - KEY_BACKUP_POLL_INTERVAL) {
             this.keyBackupInfo = await MatrixClientPeg.get().getKeyBackupVersion();
@@ -265,10 +265,10 @@ export default class DeviceListener {
             this.checkKeyBackupStatus();
         } else if (this.shouldShowSetupEncryptionToast()) {
             // make sure our keys are finished downloading
-            await cli.downloadKeys([cli.getUserId()]);
+            await cli.downloadKeys([cli.getUserId()!]);
             // cross signing isn't enabled - nag to enable it
             // There are 3 different toasts for:
-            if (!cli.getCrossSigningId() && cli.getStoredCrossSigningForUser(cli.getUserId())) {
+            if (!cli.getCrossSigningId() && cli.getStoredCrossSigningForUser(cli.getUserId()!)) {
                 // Cross-signing on account but this device doesn't trust the master key (verify this session)
                 showSetupEncryptionToast(SetupKind.VERIFY_THIS_SESSION);
                 this.checkKeyBackupStatus();
@@ -310,13 +310,13 @@ export default class DeviceListener {
         // as long as cross-signing isn't ready,
         // you can't see or dismiss any device toasts
         if (crossSigningReady) {
-            const devices = cli.getStoredDevicesForUser(cli.getUserId());
+            const devices = cli.getStoredDevicesForUser(cli.getUserId()!);
             for (const device of devices) {
                 if (device.deviceId === cli.deviceId) continue;
 
                 const deviceTrust = await cli.checkDeviceTrust(cli.getUserId()!, device.deviceId!);
                 if (!deviceTrust.isCrossSigningVerified() && !this.dismissed.has(device.deviceId)) {
-                    if (this.ourDeviceIdsAtStart.has(device.deviceId)) {
+                    if (this.ourDeviceIdsAtStart?.has(device.deviceId)) {
                         oldUnverifiedDeviceIds.add(device.deviceId);
                     } else {
                         newUnverifiedDeviceIds.add(device.deviceId);
diff --git a/src/IdentityAuthClient.tsx b/src/IdentityAuthClient.tsx
index 293a3c19a6..12f42a3add 100644
--- a/src/IdentityAuthClient.tsx
+++ b/src/IdentityAuthClient.tsx
@@ -67,7 +67,7 @@ export default class IdentityAuthClient {
         window.localStorage.setItem("mx_is_access_token", this.accessToken);
     }
 
-    private readToken(): string {
+    private readToken(): string | null {
         if (this.tempClient) return null; // temporary client: ignore
         return window.localStorage.getItem("mx_is_access_token");
     }
@@ -77,13 +77,13 @@ export default class IdentityAuthClient {
     }
 
     // Returns a promise that resolves to the access_token string from the IS
-    public async getAccessToken({ check = true } = {}): Promise<string> {
+    public async getAccessToken({ check = true } = {}): Promise<string | null> {
         if (!this.authEnabled) {
             // The current IS doesn't support authentication
             return null;
         }
 
-        let token = this.accessToken;
+        let token: string | null = this.accessToken;
         if (!token) {
             token = this.readToken();
         }
diff --git a/src/LegacyCallHandler.tsx b/src/LegacyCallHandler.tsx
index c3ca256646..34fffffc50 100644
--- a/src/LegacyCallHandler.tsx
+++ b/src/LegacyCallHandler.tsx
@@ -181,7 +181,7 @@ export default class LegacyCallHandler extends EventEmitter {
      * Gets the user-facing room associated with a call (call.roomId may be the call "virtual room"
      * if a voip_mxid_translate_pattern is set in the config)
      */
-    public roomIdForCall(call: MatrixCall): string {
+    public roomIdForCall(call?: MatrixCall): string | null {
         if (!call) return null;
 
         // check asserted identity: if we're not obeying asserted identity,
@@ -194,7 +194,7 @@ export default class LegacyCallHandler extends EventEmitter {
             }
         }
 
-        return VoipUserMapper.sharedInstance().nativeRoomForVirtualRoom(call.roomId) || call.roomId;
+        return VoipUserMapper.sharedInstance().nativeRoomForVirtualRoom(call.roomId) ?? call.roomId ?? null;
     }
 
     public start(): void {
@@ -282,7 +282,7 @@ export default class LegacyCallHandler extends EventEmitter {
     }
 
     public unSilenceCall(callId: string): void {
-        if (this.isForcedSilent) return;
+        if (this.isForcedSilent()) return;
         this.silencedCalls.delete(callId);
         this.emit(LegacyCallHandlerEvent.SilencedCallsChanged, this.silencedCalls);
         this.play(AudioID.Ring);
@@ -341,14 +341,14 @@ export default class LegacyCallHandler extends EventEmitter {
     }
 
     private shouldObeyAssertedfIdentity(): boolean {
-        return SdkConfig.getObject("voip")?.get("obey_asserted_identity");
+        return !!SdkConfig.getObject("voip")?.get("obey_asserted_identity");
     }
 
-    public getSupportsPstnProtocol(): boolean {
+    public getSupportsPstnProtocol(): boolean | null {
         return this.supportsPstnProtocol;
     }
 
-    public getSupportsVirtualRooms(): boolean {
+    public getSupportsVirtualRooms(): boolean | null {
         return this.supportsSipNativeVirtual;
     }
 
@@ -414,7 +414,7 @@ export default class LegacyCallHandler extends EventEmitter {
         cli.prepareToEncrypt(cli.getRoom(call.roomId));
     };
 
-    public getCallById(callId: string): MatrixCall {
+    public getCallById(callId: string): MatrixCall | null {
         for (const call of this.calls.values()) {
             if (call.callId === callId) return call;
         }
@@ -435,7 +435,7 @@ export default class LegacyCallHandler extends EventEmitter {
     }
 
     public getAllActiveCalls(): MatrixCall[] {
-        const activeCalls = [];
+        const activeCalls: MatrixCall[] = [];
 
         for (const call of this.calls.values()) {
             if (call.state !== CallState.Ended && call.state !== CallState.Ringing) {
@@ -446,7 +446,7 @@ export default class LegacyCallHandler extends EventEmitter {
     }
 
     public getAllActiveCallsNotInRoom(notInThisRoomId: string): MatrixCall[] {
-        const callsNotInThatRoom = [];
+        const callsNotInThatRoom: MatrixCall[] = [];
 
         for (const [roomId, call] of this.calls.entries()) {
             if (roomId !== notInThisRoomId && call.state !== CallState.Ended) {
@@ -547,7 +547,7 @@ export default class LegacyCallHandler extends EventEmitter {
         const mappedRoomId = this.roomIdForCall(call);
 
         const callForThisRoom = this.getCallForRoom(mappedRoomId);
-        return callForThisRoom && call.callId === callForThisRoom.callId;
+        return !!callForThisRoom && call.callId === callForThisRoom.callId;
     }
 
     private setCallListeners(call: MatrixCall): void {
@@ -610,7 +610,7 @@ export default class LegacyCallHandler extends EventEmitter {
                 return;
             }
 
-            const newAssertedIdentity = call.getRemoteAssertedIdentity().id;
+            const newAssertedIdentity = call.getRemoteAssertedIdentity()?.id;
             let newNativeAssertedIdentity = newAssertedIdentity;
             if (newAssertedIdentity) {
                 const response = await this.sipNativeLookup(newAssertedIdentity);
@@ -642,7 +642,7 @@ export default class LegacyCallHandler extends EventEmitter {
         });
     }
 
-    private onCallStateChanged = (newState: CallState, oldState: CallState, call: MatrixCall): void => {
+    private onCallStateChanged = (newState: CallState, oldState: CallState | null, call: MatrixCall): void => {
         if (!this.matchesCallForThisRoom(call)) return;
 
         const mappedRoomId = this.roomIdForCall(call);
@@ -830,7 +830,7 @@ export default class LegacyCallHandler extends EventEmitter {
                                     "<code>turn.matrix.org</code>, but this will not be as reliable, and " +
                                     "it will share your IP address with that server. You can also manage " +
                                     "this in Settings.",
-                                null,
+                                undefined,
                                 { code },
                             )}
                         </p>
@@ -843,7 +843,7 @@ export default class LegacyCallHandler extends EventEmitter {
                     cli.setFallbackICEServerAllowed(allow);
                 },
             },
-            null,
+            undefined,
             true,
         );
     }
@@ -882,7 +882,7 @@ export default class LegacyCallHandler extends EventEmitter {
                 title,
                 description,
             },
-            null,
+            undefined,
             true,
         );
     }
diff --git a/src/Login.ts b/src/Login.ts
index dbcdfe954e..73e6366956 100644
--- a/src/Login.ts
+++ b/src/Login.ts
@@ -29,20 +29,17 @@ interface ILoginOptions {
 }
 
 export default class Login {
-    private hsUrl: string;
-    private isUrl: string;
-    private fallbackHsUrl: string;
-    private flows: Array<LoginFlow>;
-    private defaultDeviceDisplayName: string;
-    private tempClient: MatrixClient;
+    private flows: Array<LoginFlow> = [];
+    private readonly defaultDeviceDisplayName?: string;
+    private tempClient: MatrixClient | null = null; // memoize
 
-    public constructor(hsUrl: string, isUrl: string, fallbackHsUrl?: string, opts?: ILoginOptions) {
-        this.hsUrl = hsUrl;
-        this.isUrl = isUrl;
-        this.fallbackHsUrl = fallbackHsUrl;
-        this.flows = [];
+    public constructor(
+        private hsUrl: string,
+        private isUrl: string,
+        private fallbackHsUrl: string | null,
+        opts: ILoginOptions,
+    ) {
         this.defaultDeviceDisplayName = opts.defaultDeviceDisplayName;
-        this.tempClient = null; // memoize
     }
 
     public getHomeserverUrl(): string {
@@ -96,7 +93,7 @@ export default class Login {
         phoneNumber: string | undefined,
         password: string,
     ): Promise<IMatrixClientCreds> {
-        const isEmail = username?.indexOf("@") > 0;
+        const isEmail = !!username && username.indexOf("@") > 0;
 
         let identifier;
         if (phoneCountry && phoneNumber) {
@@ -127,7 +124,7 @@ export default class Login {
         };
 
         const tryFallbackHs = (originalError: Error): Promise<IMatrixClientCreds> => {
-            return sendLoginRequest(this.fallbackHsUrl, this.isUrl, "m.login.password", loginParams).catch(
+            return sendLoginRequest(this.fallbackHsUrl!, this.isUrl, "m.login.password", loginParams).catch(
                 (fallbackError) => {
                     logger.log("fallback HS login failed", fallbackError);
                     // throw the original error
@@ -136,13 +133,13 @@ export default class Login {
             );
         };
 
-        let originalLoginError = null;
+        let originalLoginError: Error | null = null;
         return sendLoginRequest(this.hsUrl, this.isUrl, "m.login.password", loginParams)
             .catch((error) => {
                 originalLoginError = error;
                 if (error.httpStatus === 403) {
                     if (this.fallbackHsUrl) {
-                        return tryFallbackHs(originalLoginError);
+                        return tryFallbackHs(originalLoginError!);
                     }
                 }
                 throw originalLoginError;
diff --git a/src/ScalarAuthClient.ts b/src/ScalarAuthClient.ts
index 1859399d41..558e6362b9 100644
--- a/src/ScalarAuthClient.ts
+++ b/src/ScalarAuthClient.ts
@@ -256,7 +256,7 @@ export default class ScalarAuthClient {
         }
     }
 
-    public getScalarInterfaceUrlForRoom(room: Room, screen: string, id: string): string {
+    public getScalarInterfaceUrlForRoom(room: Room, screen?: string, id?: string): string {
         const roomId = room.roomId;
         const roomName = room.name;
         let url = this.uiUrl;
diff --git a/src/SecurityManager.ts b/src/SecurityManager.ts
index 73f4be06ea..2a56de8751 100644
--- a/src/SecurityManager.ts
+++ b/src/SecurityManager.ts
@@ -102,7 +102,7 @@ async function getSecretStorageKey({
 }): Promise<[string, Uint8Array]> {
     const cli = MatrixClientPeg.get();
     let keyId = await cli.getDefaultSecretStorageKeyId();
-    let keyInfo: ISecretStorageKeyInfo;
+    let keyInfo!: ISecretStorageKeyInfo;
     if (keyId) {
         // use the default SSSS key if set
         keyInfo = keyInfos[keyId];
diff --git a/src/SlashCommands.tsx b/src/SlashCommands.tsx
index e1f028bedd..66f673445d 100644
--- a/src/SlashCommands.tsx
+++ b/src/SlashCommands.tsx
@@ -82,6 +82,7 @@ const singleMxcUpload = async (): Promise<string | null> => {
         fileSelector.setAttribute("type", "file");
         fileSelector.onchange = (ev: HTMLInputEvent) => {
             const file = ev.target.files?.[0];
+            if (!file) return;
 
             Modal.createDialog(UploadConfirmDialog, {
                 file,
@@ -304,7 +305,7 @@ export const Commands = [
             if (args) {
                 const cli = MatrixClientPeg.get();
                 const room = cli.getRoom(roomId);
-                if (!room.currentState.mayClientSendStateEvent("m.room.tombstone", cli)) {
+                if (!room?.currentState.mayClientSendStateEvent("m.room.tombstone", cli)) {
                     return reject(
                         newTranslatableError("You do not have the required permissions to use this command."),
                     );
@@ -313,7 +314,7 @@ export const Commands = [
                 const { finished } = Modal.createDialog(
                     RoomUpgradeWarningDialog,
                     { roomId: roomId, targetVersion: args },
-                    /*className=*/ null,
+                    /*className=*/ undefined,
                     /*isPriority=*/ false,
                     /*isStatic=*/ true,
                 );
@@ -1199,7 +1200,7 @@ export const Commands = [
         description: _td("Switches to this room's virtual room, if it has one"),
         category: CommandCategories.advanced,
         isEnabled(): boolean {
-            return LegacyCallHandler.instance.getSupportsVirtualRooms() && !isCurrentLocalRoom();
+            return !!LegacyCallHandler.instance.getSupportsVirtualRooms() && !isCurrentLocalRoom();
         },
         runFn: (roomId) => {
             return success(
@@ -1389,7 +1390,7 @@ export function parseCommandString(input: string): { cmd?: string; args?: string
 
     const bits = input.match(/^(\S+?)(?:[ \n]+((.|\n)*))?$/);
     let cmd: string;
-    let args: string;
+    let args: string | undefined;
     if (bits) {
         cmd = bits[1].substring(1).toLowerCase();
         args = bits[2];
@@ -1414,7 +1415,7 @@ interface ICmd {
 export function getCommand(input: string): ICmd {
     const { cmd, args } = parseCommandString(input);
 
-    if (CommandMap.has(cmd) && CommandMap.get(cmd)!.isEnabled()) {
+    if (cmd && CommandMap.has(cmd) && CommandMap.get(cmd)!.isEnabled()) {
         return {
             cmd: CommandMap.get(cmd),
             args,
diff --git a/src/TextForEvent.tsx b/src/TextForEvent.tsx
index 1798a5016f..790ce2571b 100644
--- a/src/TextForEvent.tsx
+++ b/src/TextForEvent.tsx
@@ -120,20 +120,20 @@ function textForMemberEvent(ev: MatrixEvent, allowJSX: boolean, showHiddenEvents
                             // We're taking the display namke directly from the event content here so we need
                             // to strip direction override chars which the js-sdk would normally do when
                             // calculating the display name
-                            oldDisplayName: removeDirectionOverrideChars(prevContent.displayname),
-                            displayName: removeDirectionOverrideChars(content.displayname),
+                            oldDisplayName: removeDirectionOverrideChars(prevContent.displayname!),
+                            displayName: removeDirectionOverrideChars(content.displayname!),
                         });
                 } else if (!prevContent.displayname && content.displayname) {
                     return () =>
                         _t("%(senderName)s set their display name to %(displayName)s", {
                             senderName: ev.getSender(),
-                            displayName: removeDirectionOverrideChars(content.displayname),
+                            displayName: removeDirectionOverrideChars(content.displayname!),
                         });
                 } else if (prevContent.displayname && !content.displayname) {
                     return () =>
                         _t("%(senderName)s removed their display name (%(oldDisplayName)s)", {
                             senderName,
-                            oldDisplayName: removeDirectionOverrideChars(prevContent.displayname),
+                            oldDisplayName: removeDirectionOverrideChars(prevContent.displayname!),
                         });
                 } else if (prevContent.avatar_url && !content.avatar_url) {
                     return () => _t("%(senderName)s removed their profile picture", { senderName });
@@ -545,7 +545,7 @@ function textForPinnedEvent(event: MatrixEvent, allowJSX: boolean): (() => Rende
     if (newlyPinned.length === 1 && newlyUnpinned.length === 0) {
         // A single message was pinned, include a link to that message.
         if (allowJSX) {
-            const messageId = newlyPinned.pop();
+            const messageId = newlyPinned.pop()!;
 
             return () => (
                 <span>
@@ -578,7 +578,7 @@ function textForPinnedEvent(event: MatrixEvent, allowJSX: boolean): (() => Rende
     if (newlyUnpinned.length === 1 && newlyPinned.length === 0) {
         // A single message was unpinned, include a link to that message.
         if (allowJSX) {
-            const messageId = newlyUnpinned.pop();
+            const messageId = newlyUnpinned.pop()!;
 
             return () => (
                 <span>
diff --git a/src/components/structures/ContextMenu.tsx b/src/components/structures/ContextMenu.tsx
index 118e1d8d95..5e66c883e7 100644
--- a/src/components/structures/ContextMenu.tsx
+++ b/src/components/structures/ContextMenu.tsx
@@ -105,7 +105,7 @@ export interface IProps extends MenuProps {
 }
 
 interface IState {
-    contextMenuElem: HTMLDivElement;
+    contextMenuElem?: HTMLDivElement;
 }
 
 // Generic ContextMenu Portal wrapper
@@ -122,9 +122,7 @@ export default class ContextMenu extends React.PureComponent<IProps, IState> {
     public constructor(props: IProps) {
         super(props);
 
-        this.state = {
-            contextMenuElem: null,
-        };
+        this.state = {};
 
         // persist what had focus when we got initialized so we can return it after
         this.initialFocus = document.activeElement as HTMLElement;
@@ -181,7 +179,7 @@ export default class ContextMenu extends React.PureComponent<IProps, IState> {
                     button: 0, // Left
                     relatedTarget: null,
                 });
-                document.elementFromPoint(x, y).dispatchEvent(clickEvent);
+                document.elementFromPoint(x, y)?.dispatchEvent(clickEvent);
             });
         }
     };
@@ -239,7 +237,7 @@ export default class ContextMenu extends React.PureComponent<IProps, IState> {
                 // MessageActionBar), we should close any ContextMenu that is open.
                 KeyBindingAction.ArrowLeft,
                 KeyBindingAction.ArrowRight,
-            ].includes(action)
+            ].includes(action!)
         ) {
             this.props.onFinished();
         }
@@ -312,12 +310,12 @@ export default class ContextMenu extends React.PureComponent<IProps, IState> {
                 position.top = Math.min(position.top, maxTop);
                 // Adjust the chevron if necessary
                 if (chevronOffset.top !== undefined) {
-                    chevronOffset.top = propsChevronOffset + top - position.top;
+                    chevronOffset.top = propsChevronOffset! + top! - position.top;
                 }
             } else if (position.bottom !== undefined) {
                 position.bottom = Math.min(position.bottom, windowHeight - contextMenuRect.height - WINDOW_PADDING);
                 if (chevronOffset.top !== undefined) {
-                    chevronOffset.top = propsChevronOffset + position.bottom - bottom;
+                    chevronOffset.top = propsChevronOffset! + position.bottom - bottom!;
                 }
             }
             if (position.left !== undefined) {
@@ -327,12 +325,12 @@ export default class ContextMenu extends React.PureComponent<IProps, IState> {
                 }
                 position.left = Math.min(position.left, maxLeft);
                 if (chevronOffset.left !== undefined) {
-                    chevronOffset.left = propsChevronOffset + left - position.left;
+                    chevronOffset.left = propsChevronOffset! + left! - position.left;
                 }
             } else if (position.right !== undefined) {
                 position.right = Math.min(position.right, windowWidth - contextMenuRect.width - WINDOW_PADDING);
                 if (chevronOffset.left !== undefined) {
-                    chevronOffset.left = propsChevronOffset + position.right - right;
+                    chevronOffset.left = propsChevronOffset! + position.right - right!;
                 }
             }
         }
@@ -389,7 +387,7 @@ export default class ContextMenu extends React.PureComponent<IProps, IState> {
 
         const wrapperStyle: CSSProperties = {};
         if (!isNaN(Number(zIndex))) {
-            menuStyle["zIndex"] = zIndex + 1;
+            menuStyle["zIndex"] = zIndex! + 1;
             wrapperStyle["zIndex"] = zIndex;
         }
 
diff --git a/src/components/views/dialogs/InviteDialog.tsx b/src/components/views/dialogs/InviteDialog.tsx
index f1c8913da8..3084440619 100644
--- a/src/components/views/dialogs/InviteDialog.tsx
+++ b/src/components/views/dialogs/InviteDialog.tsx
@@ -97,7 +97,7 @@ class DMUserTile extends React.PureComponent<IDMUserTileProps> {
         e.preventDefault();
         e.stopPropagation();
 
-        this.props.onRemove(this.props.member);
+        this.props.onRemove!(this.props.member);
     };
 
     public render(): React.ReactNode {
@@ -132,7 +132,7 @@ class DMUserTile extends React.PureComponent<IDMUserTileProps> {
 
 interface IDMRoomTileProps {
     member: Member;
-    lastActiveTs: number;
+    lastActiveTs?: number;
     onToggle(member: Member): void;
     highlightWord: string;
     isSelected: boolean;
@@ -188,7 +188,7 @@ class DMRoomTile extends React.PureComponent<IDMRoomTileProps> {
     }
 
     public render(): React.ReactNode {
-        let timestamp = null;
+        let timestamp: JSX.Element | undefined;
         if (this.props.lastActiveTs) {
             const humanTs = humanizeTime(this.props.lastActiveTs);
             timestamp = <span className="mx_InviteDialog_tile--room_time">{humanTs}</span>;
@@ -201,7 +201,7 @@ class DMRoomTile extends React.PureComponent<IDMRoomTileProps> {
             <BaseAvatar
                 url={
                     this.props.member.getMxcAvatarUrl()
-                        ? mediaFromMxc(this.props.member.getMxcAvatarUrl()).getSquareThumbnailHttp(avatarSize)
+                        ? mediaFromMxc(this.props.member.getMxcAvatarUrl()!).getSquareThumbnailHttp(avatarSize)
                         : null
                 }
                 name={this.props.member.name}
@@ -211,7 +211,7 @@ class DMRoomTile extends React.PureComponent<IDMRoomTileProps> {
             />
         );
 
-        let checkmark = null;
+        let checkmark: JSX.Element | undefined;
         if (this.props.isSelected) {
             // To reduce flickering we put the 'selected' room tile above the real avatar
             checkmark = <div className="mx_InviteDialog_tile--room_selected" />;
@@ -301,7 +301,7 @@ interface IInviteDialogState {
 
     // These two flags are used for the 'Go' button to communicate what is going on.
     busy: boolean;
-    errorText: string;
+    errorText?: string;
 }
 
 export default class InviteDialog extends React.PureComponent<Props, IInviteDialogState> {
@@ -324,7 +324,7 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
             throw new Error("When using KIND_CALL_TRANSFER a call is required for an InviteDialog");
         }
 
-        const alreadyInvited = new Set([MatrixClientPeg.get().getUserId(), SdkConfig.get("welcome_user_id")]);
+        const alreadyInvited = new Set([MatrixClientPeg.get().getUserId()!, SdkConfig.get("welcome_user_id")]);
         if (isRoomInvite(props)) {
             const room = MatrixClientPeg.get().getRoom(props.roomId);
             if (!room) throw new Error("Room ID given to InviteDialog does not look like a room");
@@ -351,7 +351,6 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
 
             // These two flags are used for the 'Go' button to communicate what is going on.
             busy: false,
-            errorText: null,
         };
     }
 
@@ -386,7 +385,11 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
             }
         }
 
-        const recents = [];
+        const recents: {
+            userId: string;
+            user: RoomMember;
+            lastActive: number;
+        }[] = [];
         for (const userId in rooms) {
             // Filter out user IDs that are already in the room / should be excluded
             if (excludedTargetIds.has(userId)) {
@@ -455,14 +458,16 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
         // Check to see if there's anything to convert first
         if (!this.state.filterText || !this.state.filterText.includes("@")) return this.state.targets || [];
 
-        let newMember: Member;
+        let newMember: Member | undefined;
         if (this.state.filterText.startsWith("@")) {
             // Assume mxid
-            newMember = new DirectoryMember({ user_id: this.state.filterText, display_name: null, avatar_url: null });
+            newMember = new DirectoryMember({ user_id: this.state.filterText });
         } else if (SettingsStore.getValue(UIFeature.IdentityServer)) {
             // Assume email
             newMember = new ThreepidMember(this.state.filterText);
         }
+        if (!newMember) return this.state.targets;
+
         const newTargets = [...(this.state.targets || []), newMember];
         this.setState({ targets: newTargets, filterText: "" });
         return newTargets;
@@ -778,8 +783,8 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
             ...this.state.serverResultsMixin,
             ...this.state.threepidResultsMixin,
         ];
-        const toAdd = [];
-        const failed = [];
+        const toAdd: Member[] = [];
+        const failed: string[] = [];
         const potentialAddresses = text
             .split(/[\s,]+/)
             .map((p) => p.trim())
@@ -803,13 +808,11 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
 
             try {
                 const profile = await MatrixClientPeg.get().getProfileInfo(address);
-                const displayName = profile ? profile.displayname : null;
-                const avatarUrl = profile ? profile.avatar_url : null;
                 toAdd.push(
                     new DirectoryMember({
                         user_id: address,
-                        display_name: displayName,
-                        avatar_url: avatarUrl,
+                        display_name: profile?.displayname,
+                        avatar_url: profile?.avatar_url,
                     }),
                 );
             } catch (e) {
@@ -859,11 +862,11 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
         this.props.onFinished(false);
     };
 
-    private renderSection(kind: "recents" | "suggestions"): JSX.Element {
+    private renderSection(kind: "recents" | "suggestions"): ReactNode {
         let sourceMembers = kind === "recents" ? this.state.recents : this.state.suggestions;
         let showNum = kind === "recents" ? this.state.numRecentsShown : this.state.numSuggestionsShown;
         const showMoreFn = kind === "recents" ? this.showMoreRecents.bind(this) : this.showMoreSuggestions.bind(this);
-        const lastActive = (m: Result): number | null => (kind === "recents" ? m.lastActive : null);
+        const lastActive = (m: Result): number | undefined => (kind === "recents" ? m.lastActive : undefined);
         let sectionName = kind === "recents" ? _t("Recent Conversations") : _t("Suggestions");
 
         if (this.props.kind === KIND_INVITE) {
@@ -924,7 +927,7 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
         const toRender = sourceMembers.slice(0, showNum);
         const hasMore = toRender.length < sourceMembers.length;
 
-        let showMore = null;
+        let showMore: JSX.Element | undefined;
         if (hasMore) {
             showMore = (
                 <div className="mx_InviteDialog_section_showMore">
@@ -960,7 +963,7 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
             this.state.targets.length === 0 &&
             this.state.filterText.length === 0;
         const targets = this.state.targets.map((t) => (
-            <DMUserTile member={t} onRemove={!this.state.busy && this.removeMember} key={t.userId} />
+            <DMUserTile member={t} onRemove={this.state.busy ? undefined : this.removeMember} key={t.userId} />
         ));
         const input = (
             <input
@@ -973,7 +976,7 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
                 autoFocus={true}
                 disabled={this.state.busy || (this.props.kind == KIND_CALL_TRANSFER && this.state.targets.length > 0)}
                 autoComplete="off"
-                placeholder={hasPlaceholder ? _t("Search") : null}
+                placeholder={hasPlaceholder ? _t("Search") : undefined}
                 data-testid="invite-dialog-input"
             />
         );
@@ -985,7 +988,7 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
         );
     }
 
-    private renderIdentityServerWarning(): JSX.Element {
+    private renderIdentityServerWarning(): ReactNode {
         if (
             !this.state.tryingIdentityServer ||
             this.state.canUseIdentityServer ||
@@ -1080,7 +1083,7 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
         selectText(e.currentTarget);
     }
 
-    private get screenName(): ScreenName {
+    private get screenName(): ScreenName | undefined {
         switch (this.props.kind) {
             case KIND_DM:
                 return "StartChat";
@@ -1088,7 +1091,7 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
     }
 
     public render(): React.ReactNode {
-        let spinner = null;
+        let spinner: JSX.Element | undefined;
         if (this.state.busy) {
             spinner = <Spinner w={20} h={20} />;
         }
@@ -1108,7 +1111,7 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
             this.state.targets.length > 0 || (this.state.filterText && this.state.filterText.includes("@"));
 
         const cli = MatrixClientPeg.get();
-        const userId = cli.getUserId();
+        const userId = cli.getUserId()!;
         if (this.props.kind === KIND_DM) {
             title = _t("Direct Messages");
 
@@ -1150,11 +1153,11 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
                     <p>{_t("If you can't see who you're looking for, send them your invite link below.")}</p>
                 </div>
             );
-            const link = makeUserPermalink(MatrixClientPeg.get().getUserId());
+            const link = makeUserPermalink(MatrixClientPeg.get().getUserId()!);
             footer = (
                 <div className="mx_InviteDialog_footer">
                     <h3>{_t("Or send invite link")}</h3>
-                    <CopyableText getTextToCopy={() => makeUserPermalink(MatrixClientPeg.get().getUserId())}>
+                    <CopyableText getTextToCopy={() => makeUserPermalink(MatrixClientPeg.get().getUserId()!)}>
                         <a href={link} onClick={this.onLinkClick}>
                             {link}
                         </a>
@@ -1296,7 +1299,7 @@ export default class InviteDialog extends React.PureComponent<Props, IInviteDial
 
         let dialogContent;
         if (this.props.kind === KIND_CALL_TRANSFER) {
-            const tabs = [];
+            const tabs: Tab[] = [];
             tabs.push(
                 new Tab(TabId.UserDirectory, _td("User Directory"), "mx_InviteDialog_userDirectoryIcon", usersSection),
             );
diff --git a/src/components/views/dialogs/spotlight/SpotlightDialog.tsx b/src/components/views/dialogs/spotlight/SpotlightDialog.tsx
index 0102935f28..d8911876f5 100644
--- a/src/components/views/dialogs/spotlight/SpotlightDialog.tsx
+++ b/src/components/views/dialogs/spotlight/SpotlightDialog.tsx
@@ -179,7 +179,7 @@ const toPublicRoomResult = (publicRoom: IPublicRoomsChunkRoom): IPublicRoomResul
         publicRoom.name?.toLowerCase(),
         sanitizeHtml(publicRoom.topic?.toLowerCase() ?? "", { allowedTags: [] }),
         ...(publicRoom.aliases?.map((it) => it.toLowerCase()) || []),
-    ].filter(Boolean),
+    ].filter(Boolean) as string[],
 });
 
 const toRoomResult = (room: Room): IRoomResult => {
@@ -310,7 +310,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
     }, [cli]);
     const msc3946ProcessDynamicPredecessor = useFeatureEnabled("feature_dynamic_room_predecessors");
 
-    const ownInviteLink = makeUserPermalink(cli.getUserId());
+    const ownInviteLink = makeUserPermalink(cli.getUserId()!);
     const [inviteLinkCopied, setInviteLinkCopied] = useState<boolean>(false);
     const trimmedQuery = useMemo(() => query.trim(), [query]);
 
@@ -465,7 +465,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
     useWebSearchMetrics(numResults, query.length, true);
 
     const activeSpace = SpaceStore.instance.activeSpaceRoom;
-    const [spaceResults, spaceResultsLoading] = useSpaceResults(activeSpace, query);
+    const [spaceResults, spaceResultsLoading] = useSpaceResults(activeSpace ?? undefined, query);
 
     const setQuery = (e: ChangeEvent<HTMLInputElement>): void => {
         const newQuery = e.currentTarget.value;
@@ -473,7 +473,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
     };
     useEffect(() => {
         setImmediate(() => {
-            let ref: Ref;
+            let ref: Ref | undefined;
             if (rovingContext.state.refs) {
                 ref = rovingContext.state.refs[0];
             }
@@ -521,7 +521,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
         onFinished();
     };
 
-    let otherSearchesSection: JSX.Element;
+    let otherSearchesSection: JSX.Element | undefined;
     if (trimmedQuery || filter !== Filter.PublicRooms) {
         otherSearchesSection = (
             <div
@@ -693,7 +693,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
             );
         };
 
-        let peopleSection: JSX.Element;
+        let peopleSection: JSX.Element | undefined;
         if (results[Section.People].length) {
             peopleSection = (
                 <div
@@ -707,7 +707,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
             );
         }
 
-        let suggestionsSection: JSX.Element;
+        let suggestionsSection: JSX.Element | undefined;
         if (results[Section.Suggestions].length && filter === Filter.People) {
             suggestionsSection = (
                 <div
@@ -721,7 +721,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
             );
         }
 
-        let roomsSection: JSX.Element;
+        let roomsSection: JSX.Element | undefined;
         if (results[Section.Rooms].length) {
             roomsSection = (
                 <div
@@ -735,7 +735,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
             );
         }
 
-        let spacesSection: JSX.Element;
+        let spacesSection: JSX.Element | undefined;
         if (results[Section.Spaces].length) {
             spacesSection = (
                 <div
@@ -749,7 +749,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
             );
         }
 
-        let publicRoomsSection: JSX.Element;
+        let publicRoomsSection: JSX.Element | undefined;
         if (filter === Filter.PublicRooms) {
             publicRoomsSection = (
                 <div
@@ -791,7 +791,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
             );
         }
 
-        let spaceRoomsSection: JSX.Element;
+        let spaceRoomsSection: JSX.Element | undefined;
         if (spaceResults.length && activeSpace && filter === null) {
             spaceRoomsSection = (
                 <div
@@ -836,7 +836,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
             );
         }
 
-        let joinRoomSection: JSX.Element;
+        let joinRoomSection: JSX.Element | undefined;
         if (
             trimmedQuery.startsWith("#") &&
             trimmedQuery.includes(":") &&
@@ -868,7 +868,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
             );
         }
 
-        let hiddenResultsSection: JSX.Element;
+        let hiddenResultsSection: JSX.Element | undefined;
         if (filter === Filter.People) {
             hiddenResultsSection = (
                 <div className="mx_SpotlightDialog_section mx_SpotlightDialog_hiddenResults" role="group">
@@ -921,7 +921,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
             );
         }
 
-        let groupChatSection: JSX.Element;
+        let groupChatSection: JSX.Element | undefined;
         if (filter === Filter.People) {
             groupChatSection = (
                 <div
@@ -941,7 +941,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
             );
         }
 
-        let messageSearchSection: JSX.Element;
+        let messageSearchSection: JSX.Element | undefined;
         if (filter === null) {
             messageSearchSection = (
                 <div
@@ -977,7 +977,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
             </>
         );
     } else {
-        let recentSearchesSection: JSX.Element;
+        let recentSearchesSection: JSX.Element | undefined;
         if (recentSearches.length) {
             recentSearchesSection = (
                 <div
@@ -1075,7 +1075,7 @@ const SpotlightDialog: React.FC<IProps> = ({ initialText = "", initialFilter = n
                 break;
         }
 
-        let ref: RefObject<HTMLElement>;
+        let ref: RefObject<HTMLElement> | undefined;
         const accessibilityAction = getKeyBindingsManager().getAccessibilityAction(ev);
         switch (accessibilityAction) {
             case KeyBindingAction.Escape:
diff --git a/src/components/views/spaces/SpaceBasicSettings.tsx b/src/components/views/spaces/SpaceBasicSettings.tsx
index d5db0370a1..84f762d15e 100644
--- a/src/components/views/spaces/SpaceBasicSettings.tsx
+++ b/src/components/views/spaces/SpaceBasicSettings.tsx
@@ -24,11 +24,11 @@ import { chromeFileInputFix } from "../../../utils/BrowserWorkarounds";
 interface IProps {
     avatarUrl?: string;
     avatarDisabled?: boolean;
-    name?: string;
+    name: string;
     nameDisabled?: boolean;
     topic?: string;
     topicDisabled?: boolean;
-    setAvatar(avatar: File): void;
+    setAvatar(avatar?: File): void;
     setName(name: string): void;
     setTopic(topic: string): void;
 }
@@ -102,7 +102,7 @@ export const SpaceAvatar: React.FC<Pick<IProps, "avatarUrl" | "avatarDisabled" |
                     setAvatar(file);
                     const reader = new FileReader();
                     reader.onload = (ev) => {
-                        setAvatarDataUrl(ev.target.result as string);
+                        setAvatarDataUrl(ev.target?.result as string);
                     };
                     reader.readAsDataURL(file);
                 }}
diff --git a/src/components/views/spaces/SpaceChildrenPicker.tsx b/src/components/views/spaces/SpaceChildrenPicker.tsx
index 8bbf0e3868..3cf63fd0ad 100644
--- a/src/components/views/spaces/SpaceChildrenPicker.tsx
+++ b/src/components/views/spaces/SpaceChildrenPicker.tsx
@@ -53,7 +53,7 @@ const SpecificChildrenPicker: React.FC<ISpecificChildrenPickerProps> = ({
 
         const matcher = new QueryMatcher<Room>(rooms, {
             keys: ["name"],
-            funcs: [(r) => [r.getCanonicalAlias(), ...r.getAltAliases()].filter(Boolean)],
+            funcs: [(r) => [r.getCanonicalAlias(), ...r.getAltAliases()].filter(Boolean) as string[]],
             shouldMatchWordsOnly: false,
         });
 
diff --git a/src/components/views/spaces/SpaceCreateMenu.tsx b/src/components/views/spaces/SpaceCreateMenu.tsx
index 01fa0faf84..3a23b4074b 100644
--- a/src/components/views/spaces/SpaceCreateMenu.tsx
+++ b/src/components/views/spaces/SpaceCreateMenu.tsx
@@ -245,14 +245,14 @@ export const SpaceCreateForm: React.FC<ISpaceCreateFormProps> = ({
 const SpaceCreateMenu: React.FC<{
     onFinished(): void;
 }> = ({ onFinished }) => {
-    const [visibility, setVisibility] = useState<Visibility>(null);
+    const [visibility, setVisibility] = useState<Visibility | null>(null);
     const [busy, setBusy] = useState<boolean>(false);
 
     const [name, setName] = useState("");
     const spaceNameField = useRef<Field>();
     const [alias, setAlias] = useState("");
     const spaceAliasField = useRef<RoomAliasField>();
-    const [avatar, setAvatar] = useState<File>(null);
+    const [avatar, setAvatar] = useState<File | undefined>(undefined);
     const [topic, setTopic] = useState<string>("");
 
     const onSpaceCreateClick = async (e: ButtonEvent): Promise<void> => {
diff --git a/src/components/views/spaces/SpacePanel.tsx b/src/components/views/spaces/SpacePanel.tsx
index 7d3bd5bd22..92d919c5d2 100644
--- a/src/components/views/spaces/SpacePanel.tsx
+++ b/src/components/views/spaces/SpacePanel.tsx
@@ -215,7 +215,7 @@ const CreateSpaceButton: React.FC<Pick<IInnerSpacePanelProps, "isPanelCollapsed"
         }
     }, [isPanelCollapsed]); // eslint-disable-line react-hooks/exhaustive-deps
 
-    let contextMenu = null;
+    let contextMenu: JSX.Element | undefined;
     if (menuDisplayed) {
         contextMenu = <SpaceCreateMenu onFinished={closeMenu} />;
     }
diff --git a/src/components/views/spaces/SpaceTreeLevel.tsx b/src/components/views/spaces/SpaceTreeLevel.tsx
index 6e39c818d8..8338101794 100644
--- a/src/components/views/spaces/SpaceTreeLevel.tsx
+++ b/src/components/views/spaces/SpaceTreeLevel.tsx
@@ -121,11 +121,11 @@ export const SpaceButton = forwardRef<HTMLElement, IButtonProps>(
             );
         }
 
-        let contextMenu: JSX.Element;
-        if (menuDisplayed && ContextMenuComponent) {
+        let contextMenu: JSX.Element | undefined;
+        if (menuDisplayed && handle.current && ContextMenuComponent) {
             contextMenu = (
                 <ContextMenuComponent
-                    {...toRightOf(handle.current?.getBoundingClientRect(), 0)}
+                    {...toRightOf(handle.current.getBoundingClientRect(), 0)}
                     space={space}
                     onFinished={closeMenu}
                 />
@@ -242,7 +242,7 @@ export class SpaceItem extends React.PureComponent<IItemProps, IItemState> {
     }
 
     private get isCollapsed(): boolean {
-        return this.state.collapsed || this.props.isPanelCollapsed;
+        return this.state.collapsed || !!this.props.isPanelCollapsed;
     }
 
     private toggleCollapse = (evt: ButtonEvent): void => {
diff --git a/src/components/views/user-onboarding/UserOnboardingHeader.tsx b/src/components/views/user-onboarding/UserOnboardingHeader.tsx
index 77902a9aca..42ed7f0695 100644
--- a/src/components/views/user-onboarding/UserOnboardingHeader.tsx
+++ b/src/components/views/user-onboarding/UserOnboardingHeader.tsx
@@ -30,7 +30,7 @@ const onClickSendDm = (ev: ButtonEvent): void => {
 };
 
 interface Props {
-    useCase: UseCase;
+    useCase: UseCase | null;
 }
 
 export function UserOnboardingHeader({ useCase }: Props): JSX.Element {
diff --git a/src/components/views/user-onboarding/UserOnboardingPage.tsx b/src/components/views/user-onboarding/UserOnboardingPage.tsx
index 8f8be5da95..242023deb5 100644
--- a/src/components/views/user-onboarding/UserOnboardingPage.tsx
+++ b/src/components/views/user-onboarding/UserOnboardingPage.tsx
@@ -38,7 +38,7 @@ interface Props {
 // We decided to only show the new user onboarding page to new users
 // For now, that means we set the cutoff at 2022-07-01 00:00 UTC
 const USER_ONBOARDING_CUTOFF_DATE = new Date(1_656_633_600);
-export function showUserOnboardingPage(useCase: UseCase): boolean {
+export function showUserOnboardingPage(useCase: UseCase | null): boolean {
     return useCase !== null || MatrixClientPeg.userRegisteredAfter(USER_ONBOARDING_CUTOFF_DATE);
 }
 
@@ -55,13 +55,11 @@ export function UserOnboardingPage({ justRegistered = false }: Props): JSX.Eleme
     const [showList, setShowList] = useState<boolean>(false);
     useEffect(() => {
         if (initialSyncComplete) {
-            let handler: number | null = window.setTimeout(() => {
-                handler = null;
+            const handler = window.setTimeout(() => {
                 setShowList(true);
             }, ANIMATION_DURATION);
             return () => {
                 clearTimeout(handler);
-                handler = null;
             };
         } else {
             setShowList(false);
diff --git a/src/components/views/voip/DialPad.tsx b/src/components/views/voip/DialPad.tsx
index 407e0d72a6..634b88d144 100644
--- a/src/components/views/voip/DialPad.tsx
+++ b/src/components/views/voip/DialPad.tsx
@@ -18,6 +18,7 @@ import * as React from "react";
 
 import AccessibleButton, { ButtonEvent } from "../elements/AccessibleButton";
 import { _t } from "../../../languageHandler";
+import { XOR } from "../../../@types/common";
 
 const BUTTONS = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "*", "0", "#"];
 const BUTTON_LETTERS = ["", "ABC", "DEF", "GHI", "JKL", "MNO", "PQRS", "TUV", "WXYZ", "", "+", ""];
@@ -31,7 +32,7 @@ interface IButtonProps {
     kind: DialPadButtonKind;
     digit?: string;
     digitSubtext?: string;
-    onButtonPress: (digit: string, ev: ButtonEvent) => void;
+    onButtonPress: (digit: string | undefined, ev: ButtonEvent) => void;
 }
 
 class DialPadButton extends React.PureComponent<IButtonProps> {
@@ -60,16 +61,24 @@ class DialPadButton extends React.PureComponent<IButtonProps> {
     }
 }
 
-interface IProps {
+interface IBaseProps {
     onDigitPress: (digit: string, ev: ButtonEvent) => void;
-    hasDial: boolean;
     onDeletePress?: (ev: ButtonEvent) => void;
-    onDialPress?: () => void;
+    hasDial: boolean;
 }
 
-export default class Dialpad extends React.PureComponent<IProps> {
+interface IProps extends IBaseProps {
+    hasDial: false;
+}
+
+interface IDialProps extends IBaseProps {
+    hasDial: true;
+    onDialPress: () => void;
+}
+
+export default class Dialpad extends React.PureComponent<XOR<IProps, IDialProps>> {
     public render(): React.ReactNode {
-        const buttonNodes = [];
+        const buttonNodes: JSX.Element[] = [];
 
         for (let i = 0; i < BUTTONS.length; i++) {
             const button = BUTTONS[i];
diff --git a/src/components/views/voip/LegacyCallView.tsx b/src/components/views/voip/LegacyCallView.tsx
index 41ad1897a2..1e8b4621f9 100644
--- a/src/components/views/voip/LegacyCallView.tsx
+++ b/src/components/views/voip/LegacyCallView.tsx
@@ -76,7 +76,7 @@ interface IState {
     sidebarShown: boolean;
 }
 
-function getFullScreenElement(): Element | undefined {
+function getFullScreenElement(): Element | null {
     return (
         document.fullscreenElement ||
         // moz omitted because firefox supports this unprefixed now (webkit here for safari)
@@ -180,7 +180,7 @@ export default class LegacyCallView extends React.Component<IProps, IState> {
         }
     };
 
-    private updateCallListeners(oldCall: MatrixCall, newCall: MatrixCall | null): void {
+    private updateCallListeners(oldCall: MatrixCall | null, newCall: MatrixCall | null): void {
         if (oldCall === newCall) return;
 
         if (oldCall) {
@@ -245,7 +245,7 @@ export default class LegacyCallView extends React.Component<IProps, IState> {
             };
         }
 
-        let primary: CallFeed;
+        let primary: CallFeed | undefined;
 
         // Try to use a screensharing as primary, a remote one if possible
         const screensharingFeeds = feeds.filter((feed) => feed.purpose === SDPStreamMetadataPurpose.Screenshare);
@@ -289,7 +289,7 @@ export default class LegacyCallView extends React.Component<IProps, IState> {
         if (this.state.screensharing) {
             isScreensharing = await this.props.call.setScreensharingEnabled(false);
         } else {
-            if (PlatformPeg.get().supportsDesktopCapturer()) {
+            if (PlatformPeg.get()?.supportsDesktopCapturer()) {
                 const { finished } = Modal.createDialog<[string]>(DesktopCapturerSourcePicker);
                 const [source] = await finished;
                 if (!source) return;
@@ -403,7 +403,7 @@ export default class LegacyCallView extends React.Component<IProps, IState> {
         );
     }
 
-    private renderToast(): JSX.Element {
+    private renderToast(): JSX.Element | null {
         const { call } = this.props;
         const someoneIsScreensharing = call.getFeeds().some((feed) => {
             return feed.purpose === SDPStreamMetadataPurpose.Screenshare;
@@ -413,8 +413,8 @@ export default class LegacyCallView extends React.Component<IProps, IState> {
 
         const isScreensharing = call.isScreensharing();
         const { primaryFeed, sidebarShown } = this.state;
-        const sharerName = primaryFeed?.getMember().name;
-        if (!sharerName) return;
+        const sharerName = primaryFeed?.getMember()?.name;
+        if (!sharerName) return null;
 
         let text = isScreensharing ? _t("You are presenting") : _t("%(sharerName)s is presenting", { sharerName });
         if (!sidebarShown) {
@@ -495,7 +495,7 @@ export default class LegacyCallView extends React.Component<IProps, IState> {
                     );
                 } else if (isLocalOnHold) {
                     onHoldText = _t("%(peerName)s held the call", {
-                        peerName: call.getOpponentMember().name,
+                        peerName: call.getOpponentMember()?.name,
                     });
                 }
 
@@ -556,8 +556,8 @@ export default class LegacyCallView extends React.Component<IProps, IState> {
         const client = MatrixClientPeg.get();
         const callRoomId = LegacyCallHandler.instance.roomIdForCall(call);
         const secondaryCallRoomId = LegacyCallHandler.instance.roomIdForCall(secondaryCall);
-        const callRoom = client.getRoom(callRoomId);
-        const secCallRoom = secondaryCall ? client.getRoom(secondaryCallRoomId) : null;
+        const callRoom = callRoomId ? client.getRoom(callRoomId) : null;
+        const secCallRoom = secondaryCallRoomId ? client.getRoom(secondaryCallRoomId) : null;
 
         const callViewClasses = classNames({
             mx_LegacyCallView: true,
diff --git a/src/components/views/voip/LegacyCallView/LegacyCallViewButtons.tsx b/src/components/views/voip/LegacyCallView/LegacyCallViewButtons.tsx
index b7125eb6a0..0ff66fc4e8 100644
--- a/src/components/views/voip/LegacyCallView/LegacyCallViewButtons.tsx
+++ b/src/components/views/voip/LegacyCallView/LegacyCallViewButtons.tsx
@@ -104,9 +104,9 @@ const LegacyCallViewDropdownButton: React.FC<IDropdownButtonProps> = ({ state, d
                 onHover={(hovering) => setHoveringDropdown(hovering)}
                 state={state}
             />
-            {menuDisplayed && (
+            {menuDisplayed && buttonRef.current && (
                 <DeviceContextMenu
-                    {...alwaysAboveRightOf(buttonRef.current?.getBoundingClientRect())}
+                    {...alwaysAboveRightOf(buttonRef.current.getBoundingClientRect())}
                     onFinished={closeMenu}
                     deviceKinds={deviceKinds}
                 />
@@ -117,7 +117,7 @@ const LegacyCallViewDropdownButton: React.FC<IDropdownButtonProps> = ({ state, d
 
 interface IProps {
     call: MatrixCall;
-    pipMode: boolean;
+    pipMode?: boolean;
     handlers: {
         onHangupClick: () => void;
         onScreenshareClick: () => void;
@@ -150,7 +150,7 @@ interface IState {
 export default class LegacyCallViewButtons extends React.Component<IProps, IState> {
     private dialpadButton = createRef<HTMLDivElement>();
     private contextMenuButton = createRef<HTMLDivElement>();
-    private controlsHideTimer: number = null;
+    private controlsHideTimer: number | null = null;
 
     public constructor(props: IProps) {
         super(props);
@@ -223,7 +223,7 @@ export default class LegacyCallViewButtons extends React.Component<IProps, IStat
         });
 
         let dialPad;
-        if (this.state.showDialpad) {
+        if (this.state.showDialpad && this.dialpadButton.current) {
             dialPad = (
                 <DialpadContextMenu
                     {...alwaysMenuProps(
@@ -231,7 +231,7 @@ export default class LegacyCallViewButtons extends React.Component<IProps, IStat
                         ChevronFace.None,
                         CONTEXT_MENU_VPADDING,
                     )}
-                    // We mount the context menus as a as a child typically in order to include the
+                    // We mount the context menus as a child typically in order to include the
                     // context menus when fullscreening the call content.
                     // However, this does not work as well when the call is embedded in a
                     // picture-in-picture frame. Thus, only mount as child when we are *not* in PiP.
@@ -243,7 +243,7 @@ export default class LegacyCallViewButtons extends React.Component<IProps, IStat
         }
 
         let contextMenu;
-        if (this.state.showMoreMenu) {
+        if (this.state.showMoreMenu && this.contextMenuButton.current) {
             contextMenu = (
                 <LegacyCallContextMenu
                     {...alwaysMenuProps(
diff --git a/src/components/views/voip/LegacyCallView/LegacyCallViewHeader.tsx b/src/components/views/voip/LegacyCallView/LegacyCallViewHeader.tsx
index 1d20a135f1..5e18e34616 100644
--- a/src/components/views/voip/LegacyCallView/LegacyCallViewHeader.tsx
+++ b/src/components/views/voip/LegacyCallView/LegacyCallViewHeader.tsx
@@ -71,9 +71,9 @@ const SecondaryCallInfo: React.FC<ISecondaryCallInfoProps> = ({ callRoom }) => {
 };
 
 interface LegacyCallViewHeaderProps {
-    pipMode: boolean;
-    callRooms?: Room[];
-    onPipMouseDown: (event: React.MouseEvent<Element, MouseEvent>) => void;
+    pipMode?: boolean;
+    callRooms: [Room, Room | null];
+    onPipMouseDown?: (event: React.MouseEvent<Element, MouseEvent>) => void;
     onExpand?: () => void;
     onPin?: () => void;
     onMaximize?: () => void;
@@ -81,7 +81,7 @@ interface LegacyCallViewHeaderProps {
 
 const LegacyCallViewHeader: React.FC<LegacyCallViewHeaderProps> = ({
     pipMode = false,
-    callRooms = [],
+    callRooms,
     onPipMouseDown,
     onExpand,
     onPin,
diff --git a/src/components/views/voip/VideoFeed.tsx b/src/components/views/voip/VideoFeed.tsx
index 9cd0086c31..35fb851f4a 100644
--- a/src/components/views/voip/VideoFeed.tsx
+++ b/src/components/views/voip/VideoFeed.tsx
@@ -95,7 +95,7 @@ export default class VideoFeed extends React.PureComponent<IProps, IState> {
         element.addEventListener("resize", this.onResize);
     };
 
-    private updateFeed(oldFeed: CallFeed, newFeed: CallFeed): void {
+    private updateFeed(oldFeed: CallFeed | null, newFeed: CallFeed | null): void {
         if (oldFeed === newFeed) return;
 
         if (oldFeed) {
diff --git a/src/customisations/Media.ts b/src/customisations/Media.ts
index c3debef86f..9c07288b18 100644
--- a/src/customisations/Media.ts
+++ b/src/customisations/Media.ts
@@ -84,7 +84,7 @@ export class Media {
      * The HTTP URL for the thumbnail media (without any specified width, height, etc). Null/undefined
      * if no thumbnail media recorded.
      */
-    public get thumbnailHttp(): string | undefined | null {
+    public get thumbnailHttp(): string | null {
         if (!this.hasThumbnail) return null;
         // eslint-disable-next-line no-restricted-properties
         return this.client.mxcUrlToHttp(this.thumbnailMxc!);
diff --git a/src/editor/commands.tsx b/src/editor/commands.tsx
index 55dae83503..f65507054b 100644
--- a/src/editor/commands.tsx
+++ b/src/editor/commands.tsx
@@ -45,7 +45,7 @@ export function isSlashCommand(model: EditorModel): boolean {
     return false;
 }
 
-export function getSlashCommand(model: EditorModel): [Command, string, string] {
+export function getSlashCommand(model: EditorModel): [Command | undefined, string | undefined, string] {
     const commandText = model.parts.reduce((text, part) => {
         // use mxid to textify user pills in a command and room alias/id for room pills
         if (part.type === Type.UserPill || part.type === Type.RoomPill) {
@@ -69,7 +69,7 @@ export async function runSlashCommand(
     if (result.promise) {
         try {
             if (cmd.category === CommandCategories.messages || cmd.category === CommandCategories.effects) {
-                messageContent = await result.promise;
+                messageContent = (await result.promise) ?? null;
             } else {
                 await result.promise;
             }
diff --git a/src/editor/dom.ts b/src/editor/dom.ts
index 19bccdbef7..05d5789066 100644
--- a/src/editor/dom.ts
+++ b/src/editor/dom.ts
@@ -32,7 +32,7 @@ export function walkDOMDepthFirst(rootNode: Node, enterNodeCallback: Predicate,
         } else if (node.nextSibling) {
             node = node.nextSibling;
         } else {
-            while (!node.nextSibling && node !== rootNode) {
+            while (node && !node.nextSibling && node !== rootNode) {
                 node = node.parentElement;
                 if (node !== rootNode) {
                     leaveNodeCallback(node);
diff --git a/src/editor/model.ts b/src/editor/model.ts
index 975e63aa4c..83f0a232f6 100644
--- a/src/editor/model.ts
+++ b/src/editor/model.ts
@@ -127,7 +127,7 @@ export default class EditorModel {
         return this._parts;
     }
 
-    public get autoComplete(): AutocompleteWrapperModel {
+    public get autoComplete(): AutocompleteWrapperModel | null {
         if (this.activePartIdx === this.autoCompletePartIdx) {
             return this._autoComplete;
         }
@@ -212,12 +212,12 @@ export default class EditorModel {
             const transformAddedLen = this.getTransformAddedLen(newPosition, inputType, diff);
             newPosition = this.positionForOffset(caretOffset + transformAddedLen, true);
         }
-        this.updateCallback(newPosition, inputType, diff);
+        this.updateCallback?.(newPosition, inputType, diff);
         return acPromise;
     }
 
     private getTransformAddedLen(newPosition: DocumentPosition, inputType: string, diff: IDiff): number {
-        const result = this.transformCallback(newPosition, inputType, diff);
+        const result = this.transformCallback?.(newPosition, inputType, diff);
         return Number.isFinite(result) ? (result as number) : 0;
     }
 
@@ -268,13 +268,13 @@ export default class EditorModel {
         // rerender even if editor contents didn't change
         // to make sure the MessageEditor checks
         // model.autoComplete being empty and closes it
-        this.updateCallback(pos);
+        this.updateCallback?.(pos);
     };
 
     private mergeAdjacentParts(): void {
         let prevPart: Part | undefined;
         for (let i = 0; i < this._parts.length; ++i) {
-            let part = this._parts[i];
+            let part: Part | undefined = this._parts[i];
             const isEmpty = !part.text.length;
             const isMerged = !isEmpty && prevPart && prevPart.merge?.(part);
             if (isEmpty || isMerged) {
@@ -452,13 +452,13 @@ export default class EditorModel {
      */
     public transform(callback: ManualTransformCallback): Promise<void> {
         const pos = callback();
-        let acPromise: Promise<void> = null;
+        let acPromise: Promise<void> | null = null;
         if (!(pos instanceof Range)) {
             acPromise = this.setActivePart(pos, true);
         } else {
             acPromise = Promise.resolve();
         }
-        this.updateCallback(pos);
+        this.updateCallback?.(pos);
         return acPromise;
     }
 }
diff --git a/src/editor/parts.ts b/src/editor/parts.ts
index d5a5c39988..8fde5e4f84 100644
--- a/src/editor/parts.ts
+++ b/src/editor/parts.ts
@@ -422,7 +422,7 @@ class RoomPillPart extends PillPart {
 
     protected setAvatar(node: HTMLElement): void {
         let initialLetter = "";
-        let avatarUrl = Avatar.avatarUrlForRoom(this.room, 16, 16, "crop");
+        let avatarUrl = Avatar.avatarUrlForRoom(this.room ?? null, 16, 16, "crop");
         if (!avatarUrl) {
             initialLetter = Avatar.getInitialLetter(this.room?.name || this.resourceId) ?? "";
             avatarUrl = Avatar.defaultAvatarUrlForString(this.room?.roomId ?? this.resourceId);
@@ -541,7 +541,7 @@ export class PartCreator {
     public constructor(
         private readonly room: Room,
         private readonly client: MatrixClient,
-        autoCompleteCreator: AutoCompleteCreator = null,
+        autoCompleteCreator: AutoCompleteCreator | null = null,
     ) {
         // pre-create the creator as an object even without callback so it can already be passed
         // to PillCandidatePart (e.g. while deserializing) and set later on
@@ -574,7 +574,7 @@ export class PartCreator {
         return this.plain(text);
     }
 
-    public deserializePart(part: SerializedPart): Part {
+    public deserializePart(part: SerializedPart): Part | undefined {
         switch (part.type) {
             case Type.Plain:
                 return this.plain(part.text);
@@ -612,7 +612,7 @@ export class PartCreator {
     public roomPill(alias: string, roomId?: string): RoomPillPart {
         let room: Room | undefined;
         if (roomId || alias[0] !== "#") {
-            room = this.client.getRoom(roomId || alias);
+            room = this.client.getRoom(roomId || alias) ?? undefined;
         } else {
             room = this.client.getRooms().find((r) => {
                 return r.getCanonicalAlias() === alias || r.getAltAliases().includes(alias);
@@ -691,7 +691,7 @@ export class CommandPartCreator extends PartCreator {
         return new CommandPart(text, this.autoCompleteCreator);
     }
 
-    public deserializePart(part: SerializedPart): Part {
+    public deserializePart(part: SerializedPart): Part | undefined {
         if (part.type === Type.Command) {
             return this.command(part.text);
         } else {
diff --git a/src/editor/render.ts b/src/editor/render.ts
index a5c90a9077..213d68413c 100644
--- a/src/editor/render.ts
+++ b/src/editor/render.ts
@@ -93,8 +93,8 @@ function reconcileLine(lineContainer: ChildNode, parts: Part[]): void {
 
         if (needsCaretNodeBefore(part, prevPart)) {
             if (isCaretNode(currentNode as Element)) {
-                updateCaretNode(currentNode);
-                currentNode = currentNode.nextSibling;
+                updateCaretNode(currentNode!);
+                currentNode = currentNode!.nextSibling;
             } else {
                 lineContainer.insertBefore(createCaretNode(), currentNode);
             }
diff --git a/src/editor/serialize.ts b/src/editor/serialize.ts
index eb27c122dc..20ed9ab67e 100644
--- a/src/editor/serialize.ts
+++ b/src/editor/serialize.ts
@@ -63,7 +63,7 @@ interface ISerializeOpts {
 export function htmlSerializeIfNeeded(
     model: EditorModel,
     { forceHTML = false, useMarkdown = true }: ISerializeOpts = {},
-): string {
+): string | undefined {
     if (!useMarkdown) {
         return escapeHtml(textSerialize(model)).replace(/\n/g, "<br/>");
     }
@@ -72,7 +72,7 @@ export function htmlSerializeIfNeeded(
     return htmlSerializeFromMdIfNeeded(md, { forceHTML });
 }
 
-export function htmlSerializeFromMdIfNeeded(md: string, { forceHTML = false } = {}): string {
+export function htmlSerializeFromMdIfNeeded(md: string, { forceHTML = false } = {}): string | undefined {
     // copy of raw input to remove unwanted math later
     const orig = md;
 
diff --git a/src/hooks/usePublicRoomDirectory.ts b/src/hooks/usePublicRoomDirectory.ts
index eeda3480f1..e1bf806c0b 100644
--- a/src/hooks/usePublicRoomDirectory.ts
+++ b/src/hooks/usePublicRoomDirectory.ts
@@ -139,7 +139,7 @@ export const usePublicRoomDirectory = (): {
             SdkConfig.getObject("room_directory")?.get("servers")?.includes(lsRoomServer) ||
             SettingsStore.getValue("room_directory_servers")?.includes(lsRoomServer)
         ) {
-            roomServer = lsRoomServer;
+            roomServer = lsRoomServer!;
         }
 
         let instanceId: string | undefined = undefined;
diff --git a/src/hooks/useSettings.ts b/src/hooks/useSettings.ts
index 1e5ef56952..cabd4cbee9 100644
--- a/src/hooks/useSettings.ts
+++ b/src/hooks/useSettings.ts
@@ -19,7 +19,7 @@ import { useEffect, useState } from "react";
 import SettingsStore from "../settings/SettingsStore";
 
 // Hook to fetch the value of a setting and dynamically update when it changes
-export const useSettingValue = <T>(settingName: string, roomId: string = null, excludeDefault = false): T => {
+export const useSettingValue = <T>(settingName: string, roomId: string | null = null, excludeDefault = false): T => {
     const [value, setValue] = useState(SettingsStore.getValue<T>(settingName, roomId, excludeDefault));
 
     useEffect(() => {
@@ -36,7 +36,7 @@ export const useSettingValue = <T>(settingName: string, roomId: string = null, e
 };
 
 // Hook to fetch whether a feature is enabled and dynamically update when that changes
-export const useFeatureEnabled = (featureName: string, roomId: string = null): boolean => {
+export const useFeatureEnabled = (featureName: string, roomId: string | null = null): boolean => {
     const [enabled, setEnabled] = useState(SettingsStore.getValue<boolean>(featureName, roomId));
 
     useEffect(() => {
diff --git a/src/hooks/useSlidingSyncRoomSearch.ts b/src/hooks/useSlidingSyncRoomSearch.ts
index 7d5d1d92aa..c4dfbbf409 100644
--- a/src/hooks/useSlidingSyncRoomSearch.ts
+++ b/src/hooks/useSlidingSyncRoomSearch.ts
@@ -23,7 +23,7 @@ import { SlidingSyncManager } from "../SlidingSyncManager";
 
 export interface SlidingSyncRoomSearchOpts {
     limit: number;
-    query?: string;
+    query: string;
 }
 
 export const useSlidingSyncRoomSearch = (): {
@@ -55,7 +55,7 @@ export const useSlidingSyncRoomSearch = (): {
                         room_name_like: term,
                     },
                 });
-                const rooms = [];
+                const rooms: Room[] = [];
                 const { roomIndexToRoomId } = SlidingSyncManager.instance.slidingSync.getListData(
                     SlidingSyncManager.ListSearch,
                 )!;
diff --git a/src/hooks/useTimeout.ts b/src/hooks/useTimeout.ts
index 411dcf8501..df00e8bbb5 100644
--- a/src/hooks/useTimeout.ts
+++ b/src/hooks/useTimeout.ts
@@ -31,7 +31,7 @@ export const useTimeout = (handler: Handler, timeoutMs: number): void => {
     // Set up timer
     useEffect(() => {
         const timeoutID = window.setTimeout(() => {
-            savedHandler.current();
+            savedHandler.current?.();
         }, timeoutMs);
         return () => clearTimeout(timeoutID);
     }, [timeoutMs]);
@@ -50,7 +50,7 @@ export const useInterval = (handler: Handler, intervalMs: number): void => {
     // Set up timer
     useEffect(() => {
         const intervalID = window.setInterval(() => {
-            savedHandler.current();
+            savedHandler.current?.();
         }, intervalMs);
         return () => clearInterval(intervalID);
     }, [intervalMs]);
diff --git a/src/hooks/useUserDirectory.ts b/src/hooks/useUserDirectory.ts
index c256112af7..d775994e3a 100644
--- a/src/hooks/useUserDirectory.ts
+++ b/src/hooks/useUserDirectory.ts
@@ -22,7 +22,7 @@ import { useLatestResult } from "./useLatestResult";
 
 export interface IUserDirectoryOpts {
     limit: number;
-    query?: string;
+    query: string;
 }
 
 export const useUserDirectory = (): {
diff --git a/src/indexing/EventIndex.ts b/src/indexing/EventIndex.ts
index e3407e73b0..fbc528dec4 100644
--- a/src/indexing/EventIndex.ts
+++ b/src/indexing/EventIndex.ts
@@ -27,6 +27,7 @@ import { IEventWithRoomId, IMatrixProfile, IResultRoomEvents } from "matrix-js-s
 import { logger } from "matrix-js-sdk/src/logger";
 import { EventType } from "matrix-js-sdk/src/@types/event";
 import { ClientEvent, MatrixClient } from "matrix-js-sdk/src/client";
+import { ISyncStateData, SyncState } from "matrix-js-sdk/src/sync";
 
 import PlatformPeg from "../PlatformPeg";
 import { MatrixClientPeg } from "../MatrixClientPeg";
@@ -50,11 +51,11 @@ interface ICrawler {
  */
 export default class EventIndex extends EventEmitter {
     private crawlerCheckpoints: ICrawlerCheckpoint[] = [];
-    private crawler: ICrawler = null;
-    private currentCheckpoint: ICrawlerCheckpoint = null;
+    private crawler: ICrawler | null = null;
+    private currentCheckpoint: ICrawlerCheckpoint | null = null;
 
     public async init(): Promise<void> {
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
 
         this.crawlerCheckpoints = await indexManager.loadCheckpoints();
         logger.log("EventIndex: Loaded checkpoints", this.crawlerCheckpoints);
@@ -91,7 +92,7 @@ export default class EventIndex extends EventEmitter {
      * Get crawler checkpoints for the encrypted rooms and store them in the index.
      */
     public async addInitialCheckpoints(): Promise<void> {
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
         const client = MatrixClientPeg.get();
         const rooms = client.getRooms();
 
@@ -157,8 +158,8 @@ export default class EventIndex extends EventEmitter {
      *     - Every other sync, tell the event index to commit all the queued up
      *         live events
      */
-    private onSync = async (state: string, prevState: string, data: object): Promise<void> => {
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
+    private onSync = async (state: SyncState, prevState: SyncState | null, data?: ISyncStateData): Promise<void> => {
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
 
         if (prevState === "PREPARED" && state === "SYNCING") {
             // If our indexer is empty we're most likely running Element the
@@ -188,7 +189,7 @@ export default class EventIndex extends EventEmitter {
      */
     private onRoomTimeline = async (
         ev: MatrixEvent,
-        room: Room | null,
+        room: Room | undefined,
         toStartOfTimeline: boolean,
         removed: boolean,
         data: IRoomTimelineData,
@@ -198,7 +199,7 @@ export default class EventIndex extends EventEmitter {
         const client = MatrixClientPeg.get();
 
         // We only index encrypted rooms locally.
-        if (!client.isRoomEncrypted(ev.getRoomId())) return;
+        if (!client.isRoomEncrypted(ev.getRoomId()!)) return;
 
         if (ev.isRedaction()) {
             return this.redactEvent(ev);
@@ -228,7 +229,7 @@ export default class EventIndex extends EventEmitter {
      * We cannot rely on Room.redaction as this only fires if the redaction applied to an event the js-sdk has loaded.
      */
     private redactEvent = async (ev: MatrixEvent): Promise<void> => {
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
 
         try {
             await indexManager.deleteEvent(ev.getAssociatedId());
@@ -321,15 +322,15 @@ export default class EventIndex extends EventEmitter {
      * @param {MatrixEvent} ev The event that should be added to the index.
      */
     private async addLiveEventToIndex(ev: MatrixEvent): Promise<void> {
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
 
-        if (!this.isValidEvent(ev)) return;
+        if (!indexManager || !this.isValidEvent(ev)) return;
 
         const e = this.eventToJson(ev);
 
         const profile = {
-            displayname: ev.sender.rawDisplayName,
-            avatar_url: ev.sender.getMxcAvatarUrl(),
+            displayname: ev.sender?.rawDisplayName,
+            avatar_url: ev.sender?.getMxcAvatarUrl(),
         };
 
         await indexManager.addEventToIndex(e, profile);
@@ -353,7 +354,7 @@ export default class EventIndex extends EventEmitter {
     }
 
     private async addRoomCheckpoint(roomId: string, fullCrawl = false): Promise<void> {
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
         const client = MatrixClientPeg.get();
         const room = client.getRoom(roomId);
 
@@ -401,7 +402,7 @@ export default class EventIndex extends EventEmitter {
         let cancelled = false;
 
         const client = MatrixClientPeg.get();
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
 
         this.crawler = {
             cancel: () => {
@@ -649,7 +650,7 @@ export default class EventIndex extends EventEmitter {
      * task, and closes the index.
      */
     public async close(): Promise<void> {
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
         this.removeListeners();
         this.stopCrawler();
         await indexManager.closeEventIndex();
@@ -665,7 +666,7 @@ export default class EventIndex extends EventEmitter {
      * of search results once the search is done.
      */
     public async search(searchArgs: ISearchArgs): Promise<IResultRoomEvents> {
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
         return indexManager.searchEventIndex(searchArgs);
     }
 
@@ -693,11 +694,11 @@ export default class EventIndex extends EventEmitter {
     public async loadFileEvents(
         room: Room,
         limit = 10,
-        fromEvent: string = null,
+        fromEvent?: string,
         direction: string = EventTimeline.BACKWARDS,
     ): Promise<MatrixEvent[]> {
         const client = MatrixClientPeg.get();
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
 
         const loadArgs: ILoadArgs = {
             roomId: room.roomId,
@@ -790,7 +791,7 @@ export default class EventIndex extends EventEmitter {
         timeline: EventTimeline,
         room: Room,
         limit = 10,
-        fromEvent: string = null,
+        fromEvent?: string,
         direction: string = EventTimeline.BACKWARDS,
     ): Promise<boolean> {
         const matrixEvents = await this.loadFileEvents(room, limit, fromEvent, direction);
@@ -807,7 +808,7 @@ export default class EventIndex extends EventEmitter {
 
         // Add the events to the timeline of the file panel.
         matrixEvents.forEach((e) => {
-            if (!timelineSet.eventIdToTimeline(e.getId())) {
+            if (!timelineSet.eventIdToTimeline(e.getId()!)) {
                 timelineSet.addEventToTimeline(e, timeline, direction == EventTimeline.BACKWARDS);
             }
         });
@@ -817,7 +818,7 @@ export default class EventIndex extends EventEmitter {
 
         // Set the pagination token to the oldest event that we retrieved.
         if (matrixEvents.length > 0) {
-            paginationToken = matrixEvents[matrixEvents.length - 1].getId();
+            paginationToken = matrixEvents[matrixEvents.length - 1].getId()!;
             ret = true;
         }
 
@@ -878,11 +879,11 @@ export default class EventIndex extends EventEmitter {
         ): Promise<boolean> => {
             const timeline = timelineIndex.timeline;
             const timelineSet = timeline.getTimelineSet();
-            const token = timeline.getPaginationToken(direction);
+            const token = timeline.getPaginationToken(direction) ?? undefined;
 
             const ret = await this.populateFileTimeline(timelineSet, timeline, room, limit, token, direction);
 
-            timelineIndex.pendingPaginate = null;
+            timelineIndex.pendingPaginate = undefined;
             timelineWindow.extend(direction, limit);
 
             return ret;
@@ -900,9 +901,9 @@ export default class EventIndex extends EventEmitter {
      * @return {Promise<IIndexStats>} A promise that will resolve to the index
      * statistics.
      */
-    public async getStats(): Promise<IIndexStats> {
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
-        return indexManager.getStats();
+    public async getStats(): Promise<IIndexStats | undefined> {
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
+        return indexManager?.getStats();
     }
 
     /**
@@ -914,9 +915,9 @@ export default class EventIndex extends EventEmitter {
      * @return {Promise<boolean>} Returns true if the index contains events for
      * the given room, false otherwise.
      */
-    public async isRoomIndexed(roomId: string): Promise<boolean> {
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
-        return indexManager.isRoomIndexed(roomId);
+    public async isRoomIndexed(roomId: string): Promise<boolean | undefined> {
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
+        return indexManager?.isRoomIndexed(roomId);
     }
 
     /**
diff --git a/src/indexing/EventIndexPeg.ts b/src/indexing/EventIndexPeg.ts
index 77b93bf6f5..11c4696fc1 100644
--- a/src/indexing/EventIndexPeg.ts
+++ b/src/indexing/EventIndexPeg.ts
@@ -36,8 +36,8 @@ const INDEX_VERSION = 1;
  * you'll find a `EventIndex` hanging on the `EventIndexPeg`.
  */
 export class EventIndexPeg {
-    public index: EventIndex = null;
-    public error: Error = null;
+    public index: EventIndex | null = null;
+    public error: Error | null = null;
 
     private _supportIsInstalled = false;
 
@@ -49,7 +49,7 @@ export class EventIndexPeg {
      * EventIndex was successfully initialized, false otherwise.
      */
     public async init(): Promise<boolean> {
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
         if (!indexManager) {
             logger.log("EventIndex: Platform doesn't support event indexing, not initializing.");
             return false;
@@ -78,11 +78,14 @@ export class EventIndexPeg {
      */
     public async initEventIndex(): Promise<boolean> {
         const index = new EventIndex();
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
         const client = MatrixClientPeg.get();
+        if (!indexManager || !client) {
+            throw new Error("Unable to init event index");
+        }
 
-        const userId = client.getUserId();
-        const deviceId = client.getDeviceId();
+        const userId = client.getUserId()!;
+        const deviceId = client.getDeviceId()!;
 
         try {
             await indexManager.initEventIndex(userId, deviceId);
@@ -120,7 +123,7 @@ export class EventIndexPeg {
      * does not mean that support is installed.
      */
     public platformHasSupport(): boolean {
-        return PlatformPeg.get().getEventIndexingManager() !== null;
+        return PlatformPeg.get()?.getEventIndexingManager() != null;
     }
 
     /**
@@ -141,7 +144,7 @@ export class EventIndexPeg {
      *
      * @return {EventIndex} The current event index.
      */
-    public get(): EventIndex {
+    public get(): EventIndex | null {
         return this.index;
     }
 
@@ -178,9 +181,9 @@ export class EventIndexPeg {
      * deleted.
      */
     public async deleteEventIndex(): Promise<void> {
-        const indexManager = PlatformPeg.get().getEventIndexingManager();
+        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
 
-        if (indexManager !== null) {
+        if (indexManager) {
             await this.unset();
             logger.log("EventIndex: Deleting event index.");
             await indexManager.deleteEventIndex();
diff --git a/src/integrations/IntegrationManagerInstance.ts b/src/integrations/IntegrationManagerInstance.ts
index 68ca528e77..8a61705dae 100644
--- a/src/integrations/IntegrationManagerInstance.ts
+++ b/src/integrations/IntegrationManagerInstance.ts
@@ -33,18 +33,13 @@ export enum Kind {
 }
 
 export class IntegrationManagerInstance {
-    public readonly apiUrl: string;
-    public readonly uiUrl: string;
-    public readonly kind: string;
-    public readonly id: string; // only applicable in some cases
-
     // Per the spec: UI URL is optional.
-    public constructor(kind: string, apiUrl: string, uiUrl: string = apiUrl, id?: string) {
-        this.kind = kind;
-        this.apiUrl = apiUrl;
-        this.uiUrl = uiUrl;
-        this.id = id;
-    }
+    public constructor(
+        public readonly kind: string,
+        public readonly apiUrl: string,
+        public readonly uiUrl: string = apiUrl,
+        public readonly id?: string, // only applicable in some cases
+    ) {}
 
     public get name(): string {
         const parsed = url.parse(this.uiUrl);
@@ -62,7 +57,7 @@ export class IntegrationManagerInstance {
         return new ScalarAuthClient(this.apiUrl, this.uiUrl);
     }
 
-    public async open(room: Room = null, screen: string = null, integrationId: string = null): Promise<void> {
+    public async open(room: Room, screen?: string, integrationId?: string): Promise<void> {
         if (!SettingsStore.getValue("integrationProvisioning")) {
             return IntegrationManagers.sharedInstance().showDisabledDialog();
         }
diff --git a/src/integrations/IntegrationManagers.ts b/src/integrations/IntegrationManagers.ts
index 7aeaf4ab47..c1f8eb5a3c 100644
--- a/src/integrations/IntegrationManagers.ts
+++ b/src/integrations/IntegrationManagers.ts
@@ -40,7 +40,7 @@ export class IntegrationManagers {
 
     private managers: IntegrationManagerInstance[] = [];
     private client: MatrixClient;
-    private primaryManager: IntegrationManagerInstance;
+    private primaryManager: IntegrationManagerInstance | null;
 
     public static sharedInstance(): IntegrationManagers {
         if (!IntegrationManagers.instance) {
@@ -146,7 +146,7 @@ export class IntegrationManagers {
     }
 
     public getOrderedManagers(): IntegrationManagerInstance[] {
-        const ordered = [];
+        const ordered: IntegrationManagerInstance[] = [];
         for (const kind of KIND_PREFERENCE) {
             const managers = this.managers.filter((m) => m.kind === kind);
             if (!managers || !managers.length) continue;
@@ -161,7 +161,7 @@ export class IntegrationManagers {
         return ordered;
     }
 
-    public getPrimaryManager(): IntegrationManagerInstance {
+    public getPrimaryManager(): IntegrationManagerInstance | null {
         if (this.hasManager()) {
             if (this.primaryManager) return this.primaryManager;
 
@@ -195,7 +195,7 @@ export class IntegrationManagers {
      * @returns {Promise<IntegrationManagerInstance>} Resolves to an integration manager instance,
      * or null if none was found.
      */
-    public async tryDiscoverManager(domainName: string): Promise<IntegrationManagerInstance> {
+    public async tryDiscoverManager(domainName: string): Promise<IntegrationManagerInstance | null> {
         logger.log("Looking up integration manager via .well-known");
         if (domainName.startsWith("http:") || domainName.startsWith("https:")) {
             // trim off the scheme and just use the domain
diff --git a/src/languageHandler.tsx b/src/languageHandler.tsx
index 623737175d..ec37d32965 100644
--- a/src/languageHandler.tsx
+++ b/src/languageHandler.tsx
@@ -194,7 +194,7 @@ const annotateStrings = (result: TranslatedString, translationKey: string): Tran
  */
 // eslint-next-line @typescript-eslint/naming-convention
 export function _t(text: string, variables?: IVariables): string;
-export function _t(text: string, variables: IVariables, tags: Tags): React.ReactNode;
+export function _t(text: string, variables: IVariables | undefined, tags: Tags): React.ReactNode;
 export function _t(text: string, variables?: IVariables, tags?: Tags): TranslatedString {
     // The translation returns text so there's no XSS vector here (no unsafe HTML, no code execution)
     const { translated } = safeCounterpartTranslate(text, variables);
diff --git a/src/linkify-matrix.ts b/src/linkify-matrix.ts
index 64a66345ed..29258558ce 100644
--- a/src/linkify-matrix.ts
+++ b/src/linkify-matrix.ts
@@ -19,7 +19,7 @@ import * as linkifyjs from "linkifyjs";
 import { Opts, registerCustomProtocol, registerPlugin } from "linkifyjs";
 import linkifyElement from "linkify-element";
 import linkifyString from "linkify-string";
-import { RoomMember } from "matrix-js-sdk/src/models/room-member";
+import { User } from "matrix-js-sdk/src/matrix";
 
 import {
     parsePermalink,
@@ -105,13 +105,9 @@ function matrixOpaqueIdLinkifyParser({
 
 function onUserClick(event: MouseEvent, userId: string): void {
     event.preventDefault();
-    const member = new RoomMember(null, userId);
-    if (!member) {
-        return;
-    }
     dis.dispatch<ViewUserPayload>({
         action: Action.ViewUser,
-        member: member,
+        member: new User(userId),
     });
 }
 
diff --git a/src/modules/ProxiedModuleApi.ts b/src/modules/ProxiedModuleApi.ts
index 03374a7df0..56fc3ff121 100644
--- a/src/modules/ProxiedModuleApi.ts
+++ b/src/modules/ProxiedModuleApi.ts
@@ -101,10 +101,10 @@ export class ProxiedModuleApi implements ModuleApi {
         password: string,
         displayName?: string,
     ): Promise<AccountAuthInfo> {
-        const hsUrl = SdkConfig.get("validated_server_config").hsUrl;
+        const hsUrl = SdkConfig.get("validated_server_config")?.hsUrl;
         const client = Matrix.createClient({ baseUrl: hsUrl });
         const deviceName =
-            SdkConfig.get("default_device_display_name") || PlatformPeg.get().getDefaultDeviceDisplayName();
+            SdkConfig.get("default_device_display_name") || PlatformPeg.get()?.getDefaultDeviceDisplayName();
         const req: IRegisterRequestParams = {
             username,
             password,
@@ -134,9 +134,9 @@ export class ProxiedModuleApi implements ModuleApi {
 
         return {
             homeserverUrl: hsUrl,
-            userId: creds.user_id,
-            deviceId: creds.device_id,
-            accessToken: creds.access_token,
+            userId: creds.user_id!,
+            deviceId: creds.device_id!,
+            accessToken: creds.access_token!,
         };
     }
 
@@ -163,8 +163,8 @@ export class ProxiedModuleApi implements ModuleApi {
         navigateToPermalink(uri);
 
         const parts = parsePermalink(uri);
-        if (parts.roomIdOrAlias && andJoin) {
-            let roomId = parts.roomIdOrAlias;
+        if (parts?.roomIdOrAlias && andJoin) {
+            let roomId: string | undefined = parts.roomIdOrAlias;
             let servers = parts.viaServers;
             if (roomId.startsWith("#")) {
                 roomId = getCachedRoomIDForAlias(parts.roomIdOrAlias);
diff --git a/src/notifications/PushRuleVectorState.ts b/src/notifications/PushRuleVectorState.ts
index 47b4e93774..2ff504815f 100644
--- a/src/notifications/PushRuleVectorState.ts
+++ b/src/notifications/PushRuleVectorState.ts
@@ -53,6 +53,7 @@ export class PushRuleVectorState {
         } else if (pushRuleVectorState === VectorState.Loud) {
             return StandardActions.ACTION_HIGHLIGHT_DEFAULT_SOUND;
         }
+        return [];
     }
 
     /**
diff --git a/src/rageshake/rageshake.ts b/src/rageshake/rageshake.ts
index c0b538f6fb..9238e230dd 100644
--- a/src/rageshake/rageshake.ts
+++ b/src/rageshake/rageshake.ts
@@ -76,7 +76,7 @@ export class ConsoleLogger {
     }
 
     public bypassRageshake(fnName: LogFunctionName, ...args: (Error | DOMException | object | string)[]): void {
-        this.originalFunctions[fnName](...args);
+        this.originalFunctions[fnName]?.(...args);
     }
 
     public log(level: string, ...args: (Error | DOMException | object | string)[]): void {
@@ -152,7 +152,7 @@ export class IndexedDBLogStore {
             };
 
             req.onerror = () => {
-                const err = "Failed to open log database: " + req.error.name;
+                const err = "Failed to open log database: " + req.error?.name;
                 logger.error(err);
                 reject(new Error(err));
             };
@@ -234,7 +234,7 @@ export class IndexedDBLogStore {
             };
             txn.onerror = () => {
                 logger.error("Failed to flush logs : ", txn.error);
-                reject(new Error("Failed to write logs: " + txn.error.message));
+                reject(new Error("Failed to write logs: " + txn.error?.message));
             };
             objStore.add(this.generateLogEntry(lines));
             const lastModStore = txn.objectStore("logslastmod");
@@ -267,7 +267,7 @@ export class IndexedDBLogStore {
                 const query = objectStore.index("id").openCursor(IDBKeyRange.only(id), "prev");
                 let lines = "";
                 query.onerror = () => {
-                    reject(new Error("Query failed: " + query.error.message));
+                    reject(new Error("Query failed: " + query.error?.message));
                 };
                 query.onsuccess = () => {
                     const cursor = query.result;
@@ -322,7 +322,7 @@ export class IndexedDBLogStore {
                     resolve();
                 };
                 txn.onerror = () => {
-                    reject(new Error("Failed to delete logs for " + `'${id}' : ${query.error.message}`));
+                    reject(new Error("Failed to delete logs for " + `'${id}' : ${query.error?.message}`));
                 };
                 // delete last modified entries
                 const lastModStore = txn.objectStore("logslastmod");
@@ -401,14 +401,14 @@ export class IndexedDBLogStore {
  */
 function selectQuery<T>(
     store: IDBIndex | IDBObjectStore,
-    keyRange: IDBKeyRange,
+    keyRange: IDBKeyRange | undefined,
     resultMapper: (cursor: IDBCursorWithValue) => T,
 ): Promise<T[]> {
     const query = store.openCursor(keyRange);
     return new Promise((resolve, reject) => {
         const results: T[] = [];
         query.onerror = () => {
-            reject(new Error("Query failed: " + query.error.message));
+            reject(new Error("Query failed: " + query.error?.message));
         };
         // collect results
         query.onsuccess = () => {
diff --git a/src/settings/SettingsStore.ts b/src/settings/SettingsStore.ts
index ef03e96683..bcc7b14509 100644
--- a/src/settings/SettingsStore.ts
+++ b/src/settings/SettingsStore.ts
@@ -437,7 +437,7 @@ export default class SettingsStore {
         level: SettingLevel,
         roomId: string | null,
         calculatedValue: any,
-        calculatedAtLevel: SettingLevel,
+        calculatedAtLevel: SettingLevel | null,
     ): any {
         let resultingValue = calculatedValue;
 
diff --git a/src/settings/controllers/IncompatibleController.ts b/src/settings/controllers/IncompatibleController.ts
index 3621a736a4..e69848733d 100644
--- a/src/settings/controllers/IncompatibleController.ts
+++ b/src/settings/controllers/IncompatibleController.ts
@@ -36,7 +36,7 @@ export default class IncompatibleController extends SettingController {
         level: SettingLevel,
         roomId: string,
         calculatedValue: any,
-        calculatedAtLevel: SettingLevel,
+        calculatedAtLevel: SettingLevel | null,
     ): any {
         if (this.incompatibleSetting) {
             return this.forcedValue;
diff --git a/src/settings/controllers/NotificationControllers.ts b/src/settings/controllers/NotificationControllers.ts
index 6c8c351b0f..aae9b16ba2 100644
--- a/src/settings/controllers/NotificationControllers.ts
+++ b/src/settings/controllers/NotificationControllers.ts
@@ -53,7 +53,7 @@ export class NotificationsEnabledController extends SettingController {
         level: SettingLevel,
         roomId: string,
         calculatedValue: any,
-        calculatedAtLevel: SettingLevel,
+        calculatedAtLevel: SettingLevel | null,
     ): any {
         if (!getNotifier().isPossible()) return false;
 
diff --git a/src/settings/controllers/OrderedMultiController.ts b/src/settings/controllers/OrderedMultiController.ts
index 70ffa99b68..fa8535ffd6 100644
--- a/src/settings/controllers/OrderedMultiController.ts
+++ b/src/settings/controllers/OrderedMultiController.ts
@@ -35,7 +35,7 @@ export class OrderedMultiController extends SettingController {
         level: SettingLevel,
         roomId: string,
         calculatedValue: any,
-        calculatedAtLevel: SettingLevel,
+        calculatedAtLevel: SettingLevel | null,
     ): any {
         for (const controller of this.controllers) {
             const override = controller.getValueOverride(level, roomId, calculatedValue, calculatedAtLevel);
diff --git a/src/settings/controllers/ReducedMotionController.ts b/src/settings/controllers/ReducedMotionController.ts
index d98ca16513..c9f293fbd7 100644
--- a/src/settings/controllers/ReducedMotionController.ts
+++ b/src/settings/controllers/ReducedMotionController.ts
@@ -27,7 +27,7 @@ export default class ReducedMotionController extends SettingController {
         level: SettingLevel,
         roomId: string,
         calculatedValue: any,
-        calculatedAtLevel: SettingLevel,
+        calculatedAtLevel: SettingLevel | null,
     ): any {
         if (this.prefersReducedMotion()) {
             return false;
diff --git a/src/settings/controllers/SettingController.ts b/src/settings/controllers/SettingController.ts
index 725dccc623..d3a52dbb8c 100644
--- a/src/settings/controllers/SettingController.ts
+++ b/src/settings/controllers/SettingController.ts
@@ -41,7 +41,7 @@ export default abstract class SettingController {
         level: SettingLevel,
         roomId: string | null,
         calculatedValue: any,
-        calculatedAtLevel: SettingLevel,
+        calculatedAtLevel: SettingLevel | null,
     ): any {
         return null; // no override
     }
diff --git a/src/settings/controllers/ThemeController.ts b/src/settings/controllers/ThemeController.ts
index ab5410c459..9c7ce6cc7a 100644
--- a/src/settings/controllers/ThemeController.ts
+++ b/src/settings/controllers/ThemeController.ts
@@ -26,7 +26,7 @@ export default class ThemeController extends SettingController {
         level: SettingLevel,
         roomId: string,
         calculatedValue: any,
-        calculatedAtLevel: SettingLevel,
+        calculatedAtLevel: SettingLevel | null,
     ): any {
         if (!calculatedValue) return null; // Don't override null themes
 
diff --git a/src/settings/controllers/UIFeatureController.ts b/src/settings/controllers/UIFeatureController.ts
index 2748eec16a..31a2be0efc 100644
--- a/src/settings/controllers/UIFeatureController.ts
+++ b/src/settings/controllers/UIFeatureController.ts
@@ -34,7 +34,7 @@ export default class UIFeatureController extends SettingController {
         level: SettingLevel,
         roomId: string,
         calculatedValue: any,
-        calculatedAtLevel: SettingLevel,
+        calculatedAtLevel: SettingLevel | null,
     ): any {
         if (this.settingDisabled) {
             // per the docs: we force a disabled state when the feature isn't active
diff --git a/src/settings/enums/ImageSize.ts b/src/settings/enums/ImageSize.ts
index cc5596a344..28f72cb8de 100644
--- a/src/settings/enums/ImageSize.ts
+++ b/src/settings/enums/ImageSize.ts
@@ -22,7 +22,7 @@ const SIZE_LARGE = { w: 800, h: 600 };
 const SIZE_NORMAL_LANDSCAPE = { w: 324, h: 324 }; // for w > h
 const SIZE_NORMAL_PORTRAIT = { w: Math.ceil(324 * (9 / 16)), h: 324 }; // for h > w
 
-type Dimensions = { w: number; h: number };
+type Dimensions = { w?: number; h?: number };
 
 export enum ImageSize {
     Normal = "normal",
@@ -36,7 +36,7 @@ export enum ImageSize {
  * @returns {Dimensions} The suggested maximum dimensions for the image
  */
 export function suggestedSize(size: ImageSize, contentSize: Dimensions, maxHeight?: number): Dimensions {
-    const aspectRatio = contentSize.w / contentSize.h;
+    const aspectRatio = contentSize.w! / contentSize.h!;
     const portrait = aspectRatio < 1;
 
     const maxSize = size === ImageSize.Large ? SIZE_LARGE : portrait ? SIZE_NORMAL_PORTRAIT : SIZE_NORMAL_LANDSCAPE;
diff --git a/src/stores/RoomScrollStateStore.ts b/src/stores/RoomScrollStateStore.ts
index 87b48dad57..61e89ed8de 100644
--- a/src/stores/RoomScrollStateStore.ts
+++ b/src/stores/RoomScrollStateStore.ts
@@ -38,7 +38,7 @@ export class RoomScrollStateStore {
     //        from the focussedEvent.
     private scrollStateMap = new Map<string, ScrollState>();
 
-    public getScrollState(roomId: string): ScrollState {
+    public getScrollState(roomId: string): ScrollState | undefined {
         return this.scrollStateMap.get(roomId);
     }
 
diff --git a/src/stores/RoomViewStore.tsx b/src/stores/RoomViewStore.tsx
index 6dca6dce24..86f0f6bdb2 100644
--- a/src/stores/RoomViewStore.tsx
+++ b/src/stores/RoomViewStore.tsx
@@ -712,7 +712,7 @@ export class RoomViewStore extends EventEmitter {
     }
 
     // The mxEvent if one is currently being replied to/quoted
-    public getQuotingEvent(): Optional<MatrixEvent> {
+    public getQuotingEvent(): MatrixEvent | null {
         return this.state.replyingToEvent;
     }
 
diff --git a/src/stores/room-list/SlidingRoomListStore.ts b/src/stores/room-list/SlidingRoomListStore.ts
index ff2113379d..cc4de473b8 100644
--- a/src/stores/room-list/SlidingRoomListStore.ts
+++ b/src/stores/room-list/SlidingRoomListStore.ts
@@ -17,6 +17,7 @@ limitations under the License.
 import { Room } from "matrix-js-sdk/src/models/room";
 import { logger } from "matrix-js-sdk/src/logger";
 import { MSC3575Filter, SlidingSyncEvent } from "matrix-js-sdk/src/sliding-sync";
+import { Optional } from "matrix-events-sdk";
 
 import { RoomUpdateCause, TagID, OrderedDefaultTagIDs, DefaultTagID } from "./models";
 import { ITagMap, ListAlgorithm, SortAlgorithm } from "./algorithms/models";
@@ -79,12 +80,11 @@ export class SlidingRoomListStoreClass extends AsyncStoreWithClient<IState> impl
     private tagIdToSortAlgo: Record<TagID, SortAlgorithm> = {};
     private tagMap: ITagMap = {};
     private counts: Record<TagID, number> = {};
-    private stickyRoomId: string | null;
+    private stickyRoomId: Optional<string>;
 
     public constructor(dis: MatrixDispatcher, private readonly context: SdkContextClass) {
         super(dis);
         this.setMaxListeners(20); // RoomList + LeftPanel + 8xRoomSubList + spares
-        this.stickyRoomId = null;
     }
 
     public async setTagSorting(tagId: TagID, sort: SortAlgorithm): Promise<void> {
diff --git a/src/stores/room-list/previews/ReactionEventPreview.ts b/src/stores/room-list/previews/ReactionEventPreview.ts
index 6a9ae21afc..6af7ebab70 100644
--- a/src/stores/room-list/previews/ReactionEventPreview.ts
+++ b/src/stores/room-list/previews/ReactionEventPreview.ts
@@ -24,14 +24,17 @@ import SettingsStore from "../../../settings/SettingsStore";
 import DMRoomMap from "../../../utils/DMRoomMap";
 
 export class ReactionEventPreview implements IPreview {
-    public getTextFor(event: MatrixEvent, tagId?: TagID, isThread?: boolean): string {
+    public getTextFor(event: MatrixEvent, tagId?: TagID, isThread?: boolean): string | null {
         const showDms = SettingsStore.getValue("feature_roomlist_preview_reactions_dms");
         const showAll = SettingsStore.getValue("feature_roomlist_preview_reactions_all");
 
+        const roomId = event.getRoomId();
+        if (!roomId) return null; // not a room event
+
         // If we're not showing all reactions, see if we're showing DMs instead
         if (!showAll) {
             // If we're not showing reactions on DMs, or we are and the room isn't a DM, skip
-            if (!(showDms && DMRoomMap.shared().getUserIdForRoomId(event.getRoomId()))) {
+            if (!(showDms && DMRoomMap.shared().getUserIdForRoomId(roomId))) {
                 return null;
             }
         }
@@ -42,7 +45,7 @@ export class ReactionEventPreview implements IPreview {
         const reaction = relation.key;
         if (!reaction) return null; // invalid reaction (unknown format)
 
-        if (isThread || isSelf(event) || !shouldPrefixMessagesIn(event.getRoomId(), tagId)) {
+        if (isThread || isSelf(event) || !shouldPrefixMessagesIn(roomId, tagId)) {
             return reaction;
         } else {
             return _t("%(senderName)s: %(reaction)s", { senderName: getSenderName(event), reaction });
diff --git a/src/stores/room-list/previews/utils.ts b/src/stores/room-list/previews/utils.ts
index b12128943b..116e97b515 100644
--- a/src/stores/room-list/previews/utils.ts
+++ b/src/stores/room-list/previews/utils.ts
@@ -27,7 +27,7 @@ export function isSelf(event: MatrixEvent): boolean {
     return event.getSender() === selfUserId;
 }
 
-export function shouldPrefixMessagesIn(roomId: string, tagId: TagID): boolean {
+export function shouldPrefixMessagesIn(roomId: string, tagId?: TagID): boolean {
     if (tagId !== DefaultTagID.DM) return true;
 
     // We don't prefix anything in 1:1s
diff --git a/src/stores/spaces/SpaceStore.ts b/src/stores/spaces/SpaceStore.ts
index 5188af7354..3405155382 100644
--- a/src/stores/spaces/SpaceStore.ts
+++ b/src/stores/spaces/SpaceStore.ts
@@ -137,7 +137,7 @@ export class SpaceStoreClass extends AsyncStoreWithClient<IState> {
         userIdsBySpace: new Map<Room["roomId"], Set<string>>(),
     };
     // The space currently selected in the Space Panel
-    private _activeSpace?: SpaceKey = MetaSpace.Home; // set properly by onReady
+    private _activeSpace: SpaceKey = MetaSpace.Home; // set properly by onReady
     private _suggestedRooms: ISuggestedRoom[] = [];
     private _invitedSpaces = new Set<Room>();
     private spaceOrderLocalEchoMap = new Map<string, string>();
@@ -812,13 +812,13 @@ export class SpaceStoreClass extends AsyncStoreWithClient<IState> {
         const spaceDiff = mapDiff(prevChildSpacesBySpace, this.childSpacesBySpace);
         // filter out keys which changed by reference only by checking whether the sets differ
         const roomsChanged = roomDiff.changed.filter((k) => {
-            return setHasDiff(prevRoomsBySpace.get(k), this.roomIdsBySpace.get(k));
+            return setHasDiff(prevRoomsBySpace.get(k)!, this.roomIdsBySpace.get(k)!);
         });
         const usersChanged = userDiff.changed.filter((k) => {
-            return setHasDiff(prevUsersBySpace.get(k), this.userIdsBySpace.get(k));
+            return setHasDiff(prevUsersBySpace.get(k)!, this.userIdsBySpace.get(k)!);
         });
         const spacesChanged = spaceDiff.changed.filter((k) => {
-            return setHasDiff(prevChildSpacesBySpace.get(k), this.childSpacesBySpace.get(k));
+            return setHasDiff(prevChildSpacesBySpace.get(k)!, this.childSpacesBySpace.get(k)!);
         });
 
         const changeSet = new Set([
@@ -1142,9 +1142,8 @@ export class SpaceStoreClass extends AsyncStoreWithClient<IState> {
         // restore selected state from last session if any and still valid
         const lastSpaceId = window.localStorage.getItem(ACTIVE_SPACE_LS_KEY);
         const valid =
-            lastSpaceId && !isMetaSpace(lastSpaceId)
-                ? this.matrixClient.getRoom(lastSpaceId)
-                : enabledMetaSpaces[lastSpaceId];
+            lastSpaceId &&
+            (!isMetaSpace(lastSpaceId) ? this.matrixClient.getRoom(lastSpaceId) : enabledMetaSpaces[lastSpaceId]);
         if (valid) {
             // don't context switch here as it may break permalinks
             this.setActiveSpace(lastSpaceId, false);
@@ -1285,7 +1284,7 @@ export class SpaceStoreClass extends AsyncStoreWithClient<IState> {
 
     public getNotificationState(key: SpaceKey): SpaceNotificationState {
         if (this.notificationStateMap.has(key)) {
-            return this.notificationStateMap.get(key);
+            return this.notificationStateMap.get(key)!;
         }
 
         const state = new SpaceNotificationState(getRoomFn);
diff --git a/src/stores/spaces/SpaceTreeLevelLayoutStore.ts b/src/stores/spaces/SpaceTreeLevelLayoutStore.ts
index 3e5d5faa98..ced6ea5a71 100644
--- a/src/stores/spaces/SpaceTreeLevelLayoutStore.ts
+++ b/src/stores/spaces/SpaceTreeLevelLayoutStore.ts
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-const getSpaceCollapsedKey = (roomId: string, parents: Set<string>): string => {
+const getSpaceCollapsedKey = (roomId: string, parents?: Set<string>): string => {
     const separator = "/";
     let path = "";
     if (parents) {
@@ -35,12 +35,12 @@ export default class SpaceTreeLevelLayoutStore {
         return SpaceTreeLevelLayoutStore.internalInstance;
     }
 
-    public setSpaceCollapsedState(roomId: string, parents: Set<string>, collapsed: boolean): void {
+    public setSpaceCollapsedState(roomId: string, parents: Set<string> | undefined, collapsed: boolean): void {
         // XXX: localStorage doesn't allow booleans
         localStorage.setItem(getSpaceCollapsedKey(roomId, parents), collapsed.toString());
     }
 
-    public getSpaceCollapsedState(roomId: string, parents: Set<string>, fallback: boolean): boolean {
+    public getSpaceCollapsedState(roomId: string, parents: Set<string> | undefined, fallback: boolean): boolean {
         const collapsedLocalStorage = localStorage.getItem(getSpaceCollapsedKey(roomId, parents));
         // XXX: localStorage doesn't allow booleans
         return collapsedLocalStorage ? collapsedLocalStorage === "true" : fallback;
diff --git a/src/stores/widgets/StopGapWidget.ts b/src/stores/widgets/StopGapWidget.ts
index f87da3bc18..3b0a49f818 100644
--- a/src/stores/widgets/StopGapWidget.ts
+++ b/src/stores/widgets/StopGapWidget.ts
@@ -216,8 +216,8 @@ export class StopGapWidget extends EventEmitter {
         const defaults: ITemplateParams = {
             widgetRoomId: this.roomId,
             currentUserId: this.client.getUserId()!,
-            userDisplayName: OwnProfileStore.instance.displayName,
-            userHttpAvatarUrl: OwnProfileStore.instance.getHttpAvatarUrl(),
+            userDisplayName: OwnProfileStore.instance.displayName ?? undefined,
+            userHttpAvatarUrl: OwnProfileStore.instance.getHttpAvatarUrl() ?? undefined,
             clientId: ELEMENT_CLIENT_ID,
             clientTheme: SettingsStore.getValue("theme"),
             clientLanguage: getUserLanguage(),
diff --git a/src/stores/widgets/WidgetLayoutStore.ts b/src/stores/widgets/WidgetLayoutStore.ts
index 1d3b2aa1d9..a204b7d6ed 100644
--- a/src/stores/widgets/WidgetLayoutStore.ts
+++ b/src/stores/widgets/WidgetLayoutStore.ts
@@ -477,7 +477,7 @@ export class WidgetLayoutStore extends ReadyWatchingStore {
         this.updateUserLayout(room, newLayout);
     }
 
-    public hasMaximisedWidget(room: Room): boolean {
+    public hasMaximisedWidget(room?: Room): boolean {
         return this.getContainerWidgets(room, Container.Center).length > 0;
     }
 
diff --git a/src/toasts/SetupEncryptionToast.ts b/src/toasts/SetupEncryptionToast.ts
index b711cce972..3b60705ec7 100644
--- a/src/toasts/SetupEncryptionToast.ts
+++ b/src/toasts/SetupEncryptionToast.ts
@@ -85,11 +85,11 @@ export const showToast = (kind: Kind): void => {
 
     const onAccept = async (): Promise<void> => {
         if (kind === Kind.VERIFY_THIS_SESSION) {
-            Modal.createDialog(SetupEncryptionDialog, {}, null, /* priority = */ false, /* static = */ true);
+            Modal.createDialog(SetupEncryptionDialog, {}, undefined, /* priority = */ false, /* static = */ true);
         } else {
             const modal = Modal.createDialog(
                 Spinner,
-                null,
+                undefined,
                 "mx_Dialog_spinner",
                 /* priority */ false,
                 /* static */ true,
diff --git a/src/utils/IdentityServerUtils.ts b/src/utils/IdentityServerUtils.ts
index 7b820dc5c8..a9a5c754a0 100644
--- a/src/utils/IdentityServerUtils.ts
+++ b/src/utils/IdentityServerUtils.ts
@@ -19,6 +19,7 @@ import { logger } from "matrix-js-sdk/src/logger";
 
 import SdkConfig from "../SdkConfig";
 import { MatrixClientPeg } from "../MatrixClientPeg";
+import { Policies } from "../Terms";
 
 export function getDefaultIdentityServerUrl(): string {
     return SdkConfig.get("validated_server_config").isUrl;
@@ -33,7 +34,7 @@ export function setToDefaultIdentityServer(): void {
 }
 
 export async function doesIdentityServerHaveTerms(fullUrl: string): Promise<boolean> {
-    let terms;
+    let terms: { policies?: Policies } | null;
     try {
         terms = await MatrixClientPeg.get().getTerms(SERVICE_TYPES.IS, fullUrl);
     } catch (e) {
@@ -45,7 +46,7 @@ export async function doesIdentityServerHaveTerms(fullUrl: string): Promise<bool
         }
     }
 
-    return terms && terms["policies"] && Object.keys(terms["policies"]).length > 0;
+    return !!terms?.["policies"] && Object.keys(terms["policies"]).length > 0;
 }
 
 export function doesAccountDataHaveIdentityServer(): boolean {
diff --git a/src/utils/MediaEventHelper.ts b/src/utils/MediaEventHelper.ts
index 18b119b63f..2e576f9a11 100644
--- a/src/utils/MediaEventHelper.ts
+++ b/src/utils/MediaEventHelper.ts
@@ -28,12 +28,12 @@ import { IDestroyable } from "./IDestroyable";
 
 export class MediaEventHelper implements IDestroyable {
     // Either an HTTP or Object URL (when encrypted) to the media.
-    public readonly sourceUrl: LazyValue<string>;
-    public readonly thumbnailUrl: LazyValue<string>;
+    public readonly sourceUrl: LazyValue<string | null>;
+    public readonly thumbnailUrl: LazyValue<string | null>;
 
     // Either the raw or decrypted (when encrypted) contents of the file.
     public readonly sourceBlob: LazyValue<Blob>;
-    public readonly thumbnailBlob: LazyValue<Blob>;
+    public readonly thumbnailBlob: LazyValue<Blob | null>;
 
     public readonly media: Media;
 
@@ -56,12 +56,12 @@ export class MediaEventHelper implements IDestroyable {
 
     public destroy(): void {
         if (this.media.isEncrypted) {
-            if (this.sourceUrl.present) URL.revokeObjectURL(this.sourceUrl.cachedValue);
-            if (this.thumbnailUrl.present) URL.revokeObjectURL(this.thumbnailUrl.cachedValue);
+            if (this.sourceUrl.cachedValue) URL.revokeObjectURL(this.sourceUrl.cachedValue);
+            if (this.thumbnailUrl.cachedValue) URL.revokeObjectURL(this.thumbnailUrl.cachedValue);
         }
     }
 
-    private prepareSourceUrl = async (): Promise<string> => {
+    private prepareSourceUrl = async (): Promise<string | null> => {
         if (this.media.isEncrypted) {
             const blob = await this.sourceBlob.value;
             return URL.createObjectURL(blob);
@@ -70,7 +70,7 @@ export class MediaEventHelper implements IDestroyable {
         }
     };
 
-    private prepareThumbnailUrl = async (): Promise<string> => {
+    private prepareThumbnailUrl = async (): Promise<string | null> => {
         if (this.media.isEncrypted) {
             const blob = await this.thumbnailBlob.value;
             if (blob === null) return null;
@@ -83,12 +83,12 @@ export class MediaEventHelper implements IDestroyable {
     private fetchSource = (): Promise<Blob> => {
         if (this.media.isEncrypted) {
             const content = this.event.getContent<IMediaEventContent>();
-            return decryptFile(content.file, content.info);
+            return decryptFile(content.file!, content.info);
         }
         return this.media.downloadSource().then((r) => r.blob());
     };
 
-    private fetchThumbnail = (): Promise<Blob> => {
+    private fetchThumbnail = (): Promise<Blob | null> => {
         if (!this.media.hasThumbnail) return Promise.resolve(null);
 
         if (this.media.isEncrypted) {
@@ -113,7 +113,7 @@ export class MediaEventHelper implements IDestroyable {
 
         const content = event.getContent();
         const mediaMsgTypes: string[] = [MsgType.Video, MsgType.Audio, MsgType.Image, MsgType.File];
-        if (mediaMsgTypes.includes(content.msgtype)) return true;
+        if (mediaMsgTypes.includes(content.msgtype!)) return true;
         if (typeof content.url === "string") return true;
 
         // Finally, it's probably not media
diff --git a/src/utils/WidgetUtils.ts b/src/utils/WidgetUtils.ts
index e8d1dd1e32..3d4dca2fe2 100644
--- a/src/utils/WidgetUtils.ts
+++ b/src/utils/WidgetUtils.ts
@@ -96,7 +96,7 @@ export default class WidgetUtils {
      * @param  {[type]}  testUrlString URL to check
      * @return {Boolean} True if specified URL is a scalar URL
      */
-    public static isScalarUrl(testUrlString: string): boolean {
+    public static isScalarUrl(testUrlString?: string): boolean {
         if (!testUrlString) {
             logger.error("Scalar URL check failed. No URL specified");
             return false;
@@ -554,7 +554,7 @@ export default class WidgetUtils {
         // noinspection JSIgnoredPromiseFromCall
         IntegrationManagers.sharedInstance()
             .getPrimaryManager()
-            .open(room, "type_" + app.type, app.id);
+            ?.open(room, "type_" + app.type, app.id);
     }
 
     public static isManagedByManager(app: IApp): boolean {
@@ -563,7 +563,7 @@ export default class WidgetUtils {
             if (managers.hasManager()) {
                 // TODO: Pick the right manager for the widget
                 const defaultManager = managers.getPrimaryManager();
-                return WidgetUtils.isScalarUrl(defaultManager.apiUrl);
+                return WidgetUtils.isScalarUrl(defaultManager?.apiUrl);
             }
         }
         return false;
diff --git a/src/utils/beacon/useBeacon.ts b/src/utils/beacon/useBeacon.ts
index 2726262ec4..f857fc8b66 100644
--- a/src/utils/beacon/useBeacon.ts
+++ b/src/utils/beacon/useBeacon.ts
@@ -29,7 +29,7 @@ export const useBeacon = (beaconInfoEvent: MatrixEvent): Beacon | undefined => {
         const beaconIdentifier = getBeaconInfoIdentifier(beaconInfoEvent);
 
         const room = matrixClient.getRoom(roomId);
-        const beaconInstance = room.currentState.beacons.get(beaconIdentifier);
+        const beaconInstance = room?.currentState.beacons.get(beaconIdentifier);
 
         // TODO could this be less stupid?
 
diff --git a/src/utils/direct-messages.ts b/src/utils/direct-messages.ts
index 5e5a5d9c19..aede86f93b 100644
--- a/src/utils/direct-messages.ts
+++ b/src/utils/direct-messages.ts
@@ -173,7 +173,7 @@ export class ThreepidMember extends Member {
 
 export interface IDMUserTileProps {
     member: Member;
-    onRemove(member: Member): void;
+    onRemove?(member: Member): void;
 }
 
 /**
diff --git a/src/utils/dm/createDmLocalRoom.ts b/src/utils/dm/createDmLocalRoom.ts
index ed7a849a33..ac14834303 100644
--- a/src/utils/dm/createDmLocalRoom.ts
+++ b/src/utils/dm/createDmLocalRoom.ts
@@ -92,7 +92,7 @@ export async function createDmLocalRoom(client: MatrixClient, targets: Member[])
                 type: EventType.RoomMember,
                 content: {
                     displayname: target.name,
-                    avatar_url: target.getMxcAvatarUrl(),
+                    avatar_url: target.getMxcAvatarUrl() ?? undefined,
                     membership: "invite",
                     isDirect: true,
                 },
@@ -107,7 +107,7 @@ export async function createDmLocalRoom(client: MatrixClient, targets: Member[])
                 type: EventType.RoomMember,
                 content: {
                     displayname: target.name,
-                    avatar_url: target.getMxcAvatarUrl(),
+                    avatar_url: target.getMxcAvatarUrl() ?? undefined,
                     membership: "join",
                 },
                 state_key: target.userId,
diff --git a/src/utils/leave-behaviour.ts b/src/utils/leave-behaviour.ts
index 11047c5fb7..1031997724 100644
--- a/src/utils/leave-behaviour.ts
+++ b/src/utils/leave-behaviour.ts
@@ -37,7 +37,7 @@ import { bulkSpaceBehaviour } from "./space";
 import { SdkContextClass } from "../contexts/SDKContext";
 
 export async function leaveRoomBehaviour(roomId: string, retry = true, spinner = true): Promise<void> {
-    let spinnerModal: IHandle<any>;
+    let spinnerModal: IHandle<any> | undefined;
     if (spinner) {
         spinnerModal = Modal.createDialog(Spinner, undefined, "mx_Dialog_spinner");
     }
@@ -60,7 +60,7 @@ export async function leaveRoomBehaviour(roomId: string, retry = true, spinner =
         room
             .getPendingEvents()
             .filter((ev) => {
-                return [EventStatus.QUEUED, EventStatus.ENCRYPTING, EventStatus.SENDING].includes(ev.status);
+                return [EventStatus.QUEUED, EventStatus.ENCRYPTING, EventStatus.SENDING].includes(ev.status!);
             })
             .map(
                 (ev) =>
diff --git a/src/utils/location/parseGeoUri.ts b/src/utils/location/parseGeoUri.ts
index 080ff5359b..0ad4adbad9 100644
--- a/src/utils/location/parseGeoUri.ts
+++ b/src/utils/location/parseGeoUri.ts
@@ -14,8 +14,8 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-export const parseGeoUri = (uri: string): GeolocationCoordinates => {
-    function parse(s: string): number {
+export const parseGeoUri = (uri: string): GeolocationCoordinates | undefined => {
+    function parse(s: string): number | undefined {
         const ret = parseFloat(s);
         if (Number.isNaN(ret)) {
             return undefined;
@@ -28,7 +28,7 @@ export const parseGeoUri = (uri: string): GeolocationCoordinates => {
     if (!m) return;
     const parts = m[1].split(";");
     const coords = parts[0].split(",");
-    let uncertainty: number;
+    let uncertainty: number | undefined;
     for (const param of parts.slice(1)) {
         const m = param.match(/u=(.*)/);
         if (m) uncertainty = parse(m[1]);
diff --git a/src/utils/login.ts b/src/utils/login.ts
index 8e66909952..2688e0e151 100644
--- a/src/utils/login.ts
+++ b/src/utils/login.ts
@@ -23,5 +23,5 @@ export function isLoggedIn(): boolean {
     // store to hold this state.
     // See also https://github.com/vector-im/element-web/issues/15034.
     const app = window.matrixChat;
-    return app && (app as MatrixChat).state.view === Views.LOGGED_IN;
+    return (app as MatrixChat)?.state.view === Views.LOGGED_IN;
 }
diff --git a/src/utils/pillify.tsx b/src/utils/pillify.tsx
index ff21567b9c..8100b6c453 100644
--- a/src/utils/pillify.tsx
+++ b/src/utils/pillify.tsx
@@ -38,7 +38,7 @@ import { parsePermalink } from "./permalinks/Permalinks";
  *   The initial caller should pass in an empty array to seed the accumulator.
  */
 export function pillifyLinks(nodes: ArrayLike<Element>, mxEvent: MatrixEvent, pills: Element[]): void {
-    const room = MatrixClientPeg.get().getRoom(mxEvent.getRoomId());
+    const room = MatrixClientPeg.get().getRoom(mxEvent.getRoomId()) ?? undefined;
     const shouldShowPillAvatar = SettingsStore.getValue("Pill.shouldShowPillAvatar");
     let node = nodes[0];
     while (node) {
@@ -49,7 +49,7 @@ export function pillifyLinks(nodes: ArrayLike<Element>, mxEvent: MatrixEvent, pi
             node = node.nextSibling as Element;
             continue;
         } else if (node.tagName === "A" && node.getAttribute("href")) {
-            const href = node.getAttribute("href");
+            const href = node.getAttribute("href")!;
             const parts = parsePermalink(href);
             // If the link is a (localised) matrix.to link, replace it with a pill
             // We don't want to pill event permalinks, so those are ignored.
diff --git a/src/voice-broadcast/stores/VoiceBroadcastPlaybacksStore.ts b/src/voice-broadcast/stores/VoiceBroadcastPlaybacksStore.ts
index e0afea2bc1..d76241b7d1 100644
--- a/src/voice-broadcast/stores/VoiceBroadcastPlaybacksStore.ts
+++ b/src/voice-broadcast/stores/VoiceBroadcastPlaybacksStore.ts
@@ -71,17 +71,17 @@ export class VoiceBroadcastPlaybacksStore
     }
 
     public getByInfoEvent(infoEvent: MatrixEvent, client: MatrixClient): VoiceBroadcastPlayback {
-        const infoEventId = infoEvent.getId();
+        const infoEventId = infoEvent.getId()!;
 
         if (!this.playbacks.has(infoEventId)) {
             this.addPlayback(new VoiceBroadcastPlayback(infoEvent, client, this.recordings));
         }
 
-        return this.playbacks.get(infoEventId);
+        return this.playbacks.get(infoEventId)!;
     }
 
     private addPlayback(playback: VoiceBroadcastPlayback): void {
-        const infoEventId = playback.infoEvent.getId();
+        const infoEventId = playback.infoEvent.getId()!;
 
         if (this.playbacks.has(infoEventId)) return;
 
diff --git a/test/ContentMessages-test.ts b/test/ContentMessages-test.ts
index 5bfc9c315f..323cb1834b 100644
--- a/test/ContentMessages-test.ts
+++ b/test/ContentMessages-test.ts
@@ -57,7 +57,7 @@ describe("ContentMessages", () => {
             uploadContent: jest.fn().mockResolvedValue({ content_uri: "mxc://server/file" }),
         } as unknown as MatrixClient;
         contentMessages = new ContentMessages();
-        prom = Promise.resolve(null);
+        prom = Promise.resolve<ISendEventResponse>({ event_id: "$event_id" });
     });
 
     describe("sendStickerContentToRoom", () => {
@@ -98,7 +98,7 @@ describe("ContentMessages", () => {
             mocked(doMaybeLocalRoomAction).mockImplementation(
                 <T>(roomId: string, fn: (actualRoomId: string) => Promise<T>) => fn(roomId),
             );
-            mocked(BlurhashEncoder.instance.getBlurhash).mockResolvedValue(undefined);
+            mocked(BlurhashEncoder.instance.getBlurhash).mockResolvedValue("blurhashstring");
         });
 
         it("should use m.image for image files", async () => {
@@ -134,7 +134,7 @@ describe("ContentMessages", () => {
                 const element = createElement(tagName);
                 if (tagName === "video") {
                     (<HTMLVideoElement>element).load = jest.fn();
-                    (<HTMLVideoElement>element).play = () => element.onloadeddata(new Event("loadeddata"));
+                    (<HTMLVideoElement>element).play = () => element.onloadeddata!(new Event("loadeddata"));
                     (<HTMLVideoElement>element).pause = jest.fn();
                     Object.defineProperty(element, "videoHeight", {
                         get() {
@@ -200,8 +200,8 @@ describe("ContentMessages", () => {
 
             expect(upload.loaded).toBe(0);
             expect(upload.total).toBe(file.size);
-            const { progressHandler } = mocked(client.uploadContent).mock.calls[0][1];
-            progressHandler({ loaded: 123, total: 1234 });
+            const { progressHandler } = mocked(client.uploadContent).mock.calls[0][1]!;
+            progressHandler!({ loaded: 123, total: 1234 });
             expect(upload.loaded).toBe(123);
             expect(upload.total).toBe(1234);
             await prom;
@@ -256,11 +256,11 @@ describe("ContentMessages", () => {
             mocked(client.uploadContent).mockReturnValue(deferred.promise);
             const file1 = new File([], "file1");
             const prom = contentMessages.sendContentToRoom(file1, roomId, undefined, client, undefined);
-            const { abortController } = mocked(client.uploadContent).mock.calls[0][1];
-            expect(abortController.signal.aborted).toBeFalsy();
+            const { abortController } = mocked(client.uploadContent).mock.calls[0][1]!;
+            expect(abortController!.signal.aborted).toBeFalsy();
             const [upload] = contentMessages.getCurrentUploads();
             contentMessages.cancelUpload(upload);
-            expect(abortController.signal.aborted).toBeTruthy();
+            expect(abortController!.signal.aborted).toBeTruthy();
             deferred.resolve({} as UploadResponse);
             await prom;
         });
@@ -325,7 +325,7 @@ describe("uploadFile", () => {
         const file = new Blob([]);
 
         const prom = uploadFile(client, "!roomId:server", file);
-        mocked(client.uploadContent).mock.calls[0][1].abortController.abort();
+        mocked(client.uploadContent).mock.calls[0][1]!.abortController!.abort();
         deferred.resolve({ content_uri: "mxc://foo/bar" });
         await expect(prom).rejects.toThrowError(UploadCanceledError);
     });
diff --git a/test/Reply-test.ts b/test/Reply-test.ts
index 4ae7f6fa82..358e34e540 100644
--- a/test/Reply-test.ts
+++ b/test/Reply-test.ts
@@ -134,12 +134,14 @@ But this is not
             expect(getNestedReplyText(event, mockPermalinkGenerator)).toMatchSnapshot();
         });
 
-        [
-            ["m.room.message", MsgType.Location, LocationAssetType.Pin],
-            ["m.room.message", MsgType.Location, LocationAssetType.Self],
-            [M_BEACON_INFO.name, undefined, LocationAssetType.Pin],
-            [M_BEACON_INFO.name, undefined, LocationAssetType.Self],
-        ].forEach(([type, msgType, assetType]) => {
+        (
+            [
+                ["m.room.message", MsgType.Location, LocationAssetType.Pin],
+                ["m.room.message", MsgType.Location, LocationAssetType.Self],
+                [M_BEACON_INFO.name, undefined, LocationAssetType.Pin],
+                [M_BEACON_INFO.name, undefined, LocationAssetType.Self],
+            ] as const
+        ).forEach(([type, msgType, assetType]) => {
             it(`should create the expected fallback text for ${assetType} ${type}/${msgType}`, () => {
                 const event = makeTestEvent(type, {
                     body: "body",
diff --git a/test/Terms-test.tsx b/test/Terms-test.tsx
index e96d4f253d..7d02c3fe66 100644
--- a/test/Terms-test.tsx
+++ b/test/Terms-test.tsx
@@ -49,7 +49,7 @@ describe("Terms", function () {
 
     beforeEach(function () {
         jest.clearAllMocks();
-        mockClient.getAccountData.mockReturnValue(null);
+        mockClient.getAccountData.mockReturnValue(undefined);
         mockClient.getTerms.mockResolvedValue(null);
         mockClient.setAccountData.mockResolvedValue({});
     });
@@ -59,7 +59,7 @@ describe("Terms", function () {
     });
 
     it("should prompt for all terms & services if no account data", async function () {
-        mockClient.getAccountData.mockReturnValue(null);
+        mockClient.getAccountData.mockReturnValue(undefined);
         mockClient.getTerms.mockResolvedValue({
             policies: {
                 policy_the_first: POLICY_ONE,
diff --git a/test/components/structures/RoomStatusBar-test.tsx b/test/components/structures/RoomStatusBar-test.tsx
index aad8251c2a..a11bd899d3 100644
--- a/test/components/structures/RoomStatusBar-test.tsx
+++ b/test/components/structures/RoomStatusBar-test.tsx
@@ -34,7 +34,7 @@ describe("RoomStatusBar", () => {
 
         stubClient();
         client = MatrixClientPeg.get();
-        room = new Room(ROOM_ID, client, client.getUserId(), {
+        room = new Room(ROOM_ID, client, client.getUserId()!, {
             pendingEventOrdering: PendingEventOrdering.Detached,
         });
         event = mkEvent({
@@ -72,7 +72,7 @@ describe("RoomStatusBar", () => {
                 length: 2,
             });
             rootEvent.status = EventStatus.NOT_SENT;
-            room.addPendingEvent(rootEvent, rootEvent.getId());
+            room.addPendingEvent(rootEvent, rootEvent.getId()!);
             for (const event of events) {
                 event.status = EventStatus.NOT_SENT;
                 room.addPendingEvent(event, Date.now() + Math.random() + "");
diff --git a/test/components/structures/ThreadView-test.tsx b/test/components/structures/ThreadView-test.tsx
index 31ec611557..2993a3b6d6 100644
--- a/test/components/structures/ThreadView-test.tsx
+++ b/test/components/structures/ThreadView-test.tsx
@@ -99,10 +99,10 @@ describe("ThreadView", () => {
                 "is_falling_back": true,
                 "m.in_reply_to": {
                     event_id: rootEvent
-                        .getThread()
+                        .getThread()!
                         .lastReply((ev: MatrixEvent) => {
                             return ev.isRelation(THREAD_RELATION_TYPE.name);
-                        })
+                        })!
                         .getId(),
                 },
                 "rel_type": RelationType.Thread,
@@ -126,8 +126,8 @@ describe("ThreadView", () => {
         const res = mkThread({
             room,
             client: mockClient,
-            authorId: mockClient.getUserId(),
-            participantUserIds: [mockClient.getUserId()],
+            authorId: mockClient.getUserId()!,
+            participantUserIds: [mockClient.getUserId()!],
         });
 
         rootEvent = res.rootEvent;
@@ -154,8 +154,8 @@ describe("ThreadView", () => {
         const { rootEvent: rootEvent2 } = mkThread({
             room,
             client: mockClient,
-            authorId: mockClient.getUserId(),
-            participantUserIds: [mockClient.getUserId()],
+            authorId: mockClient.getUserId()!,
+            participantUserIds: [mockClient.getUserId()!],
         });
 
         act(() => {
diff --git a/test/components/views/context_menus/ThreadListContextMenu-test.tsx b/test/components/views/context_menus/ThreadListContextMenu-test.tsx
index 74c74addc5..2f1c5df7f5 100644
--- a/test/components/views/context_menus/ThreadListContextMenu-test.tsx
+++ b/test/components/views/context_menus/ThreadListContextMenu-test.tsx
@@ -54,8 +54,8 @@ describe("ThreadListContextMenu", () => {
         const res = mkThread({
             room,
             client: mockClient,
-            authorId: mockClient.getUserId(),
-            participantUserIds: [mockClient.getUserId()],
+            authorId: mockClient.getUserId()!,
+            participantUserIds: [mockClient.getUserId()!],
         });
 
         event = res.rootEvent;
diff --git a/test/components/views/dialogs/ExportDialog-test.tsx b/test/components/views/dialogs/ExportDialog-test.tsx
index 9e4d0148dc..afc490546f 100644
--- a/test/components/views/dialogs/ExportDialog-test.tsx
+++ b/test/components/views/dialogs/ExportDialog-test.tsx
@@ -109,7 +109,7 @@ describe("<ExportDialog />", () => {
         plainTextExporterInstance.export.mockClear();
 
         // default setting value
-        ChatExportMock.getForceChatExportParameters.mockClear().mockReturnValue({});
+        mocked(ChatExportMock.getForceChatExportParameters!).mockClear().mockReturnValue({});
     });
 
     it("renders export dialog", () => {
@@ -145,7 +145,7 @@ describe("<ExportDialog />", () => {
     });
 
     it("exports room using values set from ForceRoomExportParameters", async () => {
-        ChatExportMock.getForceChatExportParameters.mockReturnValue({
+        mocked(ChatExportMock.getForceChatExportParameters!).mockReturnValue({
             format: ExportFormat.PlainText,
             range: ExportType.Beginning,
             sizeMb: 7000,
@@ -198,7 +198,7 @@ describe("<ExportDialog />", () => {
         });
 
         it("does not render export format when set in ForceRoomExportParameters", () => {
-            ChatExportMock.getForceChatExportParameters.mockReturnValue({
+            mocked(ChatExportMock.getForceChatExportParameters!).mockReturnValue({
                 format: ExportFormat.PlainText,
             });
             const component = getComponent();
@@ -219,7 +219,7 @@ describe("<ExportDialog />", () => {
         });
 
         it("does not render export type when set in ForceRoomExportParameters", () => {
-            ChatExportMock.getForceChatExportParameters.mockReturnValue({
+            mocked(ChatExportMock.getForceChatExportParameters!).mockReturnValue({
                 range: ExportType.Beginning,
             });
             const component = getComponent();
@@ -310,7 +310,7 @@ describe("<ExportDialog />", () => {
         });
 
         it("does not render size limit input when set in ForceRoomExportParameters", () => {
-            ChatExportMock.getForceChatExportParameters.mockReturnValue({
+            mocked(ChatExportMock.getForceChatExportParameters!).mockReturnValue({
                 sizeMb: 10000,
             });
             const component = getComponent();
@@ -321,7 +321,7 @@ describe("<ExportDialog />", () => {
          * 2000mb size limit does not apply when higher limit is configured in config
          */
         it("exports when size limit set in ForceRoomExportParameters is larger than 2000", async () => {
-            ChatExportMock.getForceChatExportParameters.mockReturnValue({
+            mocked(ChatExportMock.getForceChatExportParameters!).mockReturnValue({
                 sizeMb: 10000,
             });
             const component = getComponent();
@@ -344,7 +344,7 @@ describe("<ExportDialog />", () => {
         });
 
         it("does not render input when set in ForceRoomExportParameters", () => {
-            ChatExportMock.getForceChatExportParameters.mockReturnValue({
+            mocked(ChatExportMock.getForceChatExportParameters!).mockReturnValue({
                 includeAttachments: false,
             });
             const component = getComponent();
diff --git a/test/components/views/settings/DevicesPanel-test.tsx b/test/components/views/settings/DevicesPanel-test.tsx
index 3565e59c43..530bf55a79 100644
--- a/test/components/views/settings/DevicesPanel-test.tsx
+++ b/test/components/views/settings/DevicesPanel-test.tsx
@@ -74,7 +74,7 @@ describe("<DevicesPanel />", () => {
 
         const toggleDeviceSelection = (container: HTMLElement, deviceId: string) =>
             act(() => {
-                const checkbox = container.querySelector(`#device-tile-checkbox-${deviceId}`);
+                const checkbox = container.querySelector(`#device-tile-checkbox-${deviceId}`)!;
                 fireEvent.click(checkbox);
             });
 
@@ -204,7 +204,7 @@ describe("<DevicesPanel />", () => {
 
             // close the modal without submission
             act(() => {
-                const modalCloseButton = document.querySelector('[aria-label="Close dialog"]');
+                const modalCloseButton = document.querySelector('[aria-label="Close dialog"]')!;
                 fireEvent.click(modalCloseButton);
             });
 
diff --git a/test/components/views/settings/tabs/user/PreferencesUserSettingsTab-test.tsx b/test/components/views/settings/tabs/user/PreferencesUserSettingsTab-test.tsx
index 0e69f1878c..4f7441f59a 100644
--- a/test/components/views/settings/tabs/user/PreferencesUserSettingsTab-test.tsx
+++ b/test/components/views/settings/tabs/user/PreferencesUserSettingsTab-test.tsx
@@ -49,6 +49,7 @@ describe("PreferencesUserSettingsTab", () => {
             const client = MatrixClientPeg.get();
             jest.spyOn(client, "isVersionSupported").mockImplementation(async (version: string) => {
                 if (version === "v1.4") return val;
+                return false;
             });
         };
 
@@ -61,8 +62,12 @@ describe("PreferencesUserSettingsTab", () => {
             };
         };
 
-        const expectSetValueToHaveBeenCalled = (name: string, roomId: string, level: SettingLevel, value: boolean) =>
-            expect(SettingsStore.setValue).toHaveBeenCalledWith(name, roomId, level, value);
+        const expectSetValueToHaveBeenCalled = (
+            name: string,
+            roomId: string | undefined,
+            level: SettingLevel,
+            value: boolean,
+        ) => expect(SettingsStore.setValue).toHaveBeenCalledWith(name, roomId, level, value);
 
         describe("with server support", () => {
             beforeEach(() => {
diff --git a/test/models/Call-test.ts b/test/models/Call-test.ts
index 2f01f06636..028cf12018 100644
--- a/test/models/Call-test.ts
+++ b/test/models/Call-test.ts
@@ -923,7 +923,7 @@ describe("ElementCall", () => {
                 jest.spyOn(Modal, "createDialog").mockReturnValue({
                     finished: new Promise((r) => r([sourceId])),
                 } as IHandle<any[]>);
-                jest.spyOn(PlatformPeg.get(), "supportsDesktopCapturer").mockReturnValue(true);
+                jest.spyOn(PlatformPeg.get()!, "supportsDesktopCapturer").mockReturnValue(true);
 
                 await call.connect();
 
@@ -951,7 +951,7 @@ describe("ElementCall", () => {
                 jest.spyOn(Modal, "createDialog").mockReturnValue({
                     finished: new Promise((r) => r([null])),
                 } as IHandle<any[]>);
-                jest.spyOn(PlatformPeg.get(), "supportsDesktopCapturer").mockReturnValue(true);
+                jest.spyOn(PlatformPeg.get()!, "supportsDesktopCapturer").mockReturnValue(true);
 
                 await call.connect();
 
@@ -976,7 +976,7 @@ describe("ElementCall", () => {
             });
 
             it("replies with pending: false if we don't support desktop capturer", async () => {
-                jest.spyOn(PlatformPeg.get(), "supportsDesktopCapturer").mockReturnValue(false);
+                jest.spyOn(PlatformPeg.get()!, "supportsDesktopCapturer").mockReturnValue(false);
 
                 await call.connect();
 
diff --git a/test/settings/enums/ImageSize-test.ts b/test/settings/enums/ImageSize-test.ts
index 0eb89a45bb..9103bb7307 100644
--- a/test/settings/enums/ImageSize-test.ts
+++ b/test/settings/enums/ImageSize-test.ts
@@ -31,7 +31,7 @@ describe("ImageSize", () => {
             expect(size).toStrictEqual({ w: 800, h: 400 });
         });
         it("returns max values if content size is not specified", () => {
-            const size = suggestedSize(ImageSize.Normal, { w: null, h: null });
+            const size = suggestedSize(ImageSize.Normal, {});
             expect(size).toStrictEqual({ w: 324, h: 324 });
         });
         it("returns integer values", () => {
diff --git a/test/stores/OwnBeaconStore-test.ts b/test/stores/OwnBeaconStore-test.ts
index afe48edd32..79ff78530e 100644
--- a/test/stores/OwnBeaconStore-test.ts
+++ b/test/stores/OwnBeaconStore-test.ts
@@ -102,9 +102,9 @@ describe("OwnBeaconStore", () => {
     };
 
     const expireBeaconAndEmit = (store: OwnBeaconStore, beaconInfoEvent: MatrixEvent): void => {
-        const beacon = store.getBeaconById(getBeaconInfoIdentifier(beaconInfoEvent));
+        const beacon = store.getBeaconById(getBeaconInfoIdentifier(beaconInfoEvent))!;
         // time travel until beacon is expired
-        advanceDateAndTime(beacon.beaconInfo.timeout + 100);
+        advanceDateAndTime(beacon.beaconInfo!.timeout + 100);
 
         // force an update on the beacon
         // @ts-ignore
@@ -118,13 +118,13 @@ describe("OwnBeaconStore", () => {
         beaconInfoEvent: MatrixEvent,
         isLive: boolean,
     ): void => {
-        const beacon = store.getBeaconById(getBeaconInfoIdentifier(beaconInfoEvent));
+        const beacon = store.getBeaconById(getBeaconInfoIdentifier(beaconInfoEvent))!;
         // matches original state of event content
         // except for live property
         const updateEvent = makeBeaconInfoEvent(
-            beaconInfoEvent.getSender(),
-            beaconInfoEvent.getRoomId(),
-            { isLive, timeout: beacon.beaconInfo.timeout },
+            beaconInfoEvent.getSender()!,
+            beaconInfoEvent.getRoomId()!,
+            { isLive, timeout: beacon.beaconInfo!.timeout },
             "update-event-id",
         );
         beacon.update(updateEvent);
@@ -236,12 +236,12 @@ describe("OwnBeaconStore", () => {
             expect(mockClient.sendEvent).toHaveBeenCalledWith(
                 room1Id,
                 M_BEACON.name,
-                makeBeaconContent(defaultLocationUri, now, alicesRoom1BeaconInfo.getId()),
+                makeBeaconContent(defaultLocationUri, now, alicesRoom1BeaconInfo.getId()!),
             );
             expect(mockClient.sendEvent).toHaveBeenCalledWith(
                 room2Id,
                 M_BEACON.name,
-                makeBeaconContent(defaultLocationUri, now, alicesRoom2BeaconInfo.getId()),
+                makeBeaconContent(defaultLocationUri, now, alicesRoom2BeaconInfo.getId()!),
             );
         });
     });
@@ -263,7 +263,7 @@ describe("OwnBeaconStore", () => {
         it("destroys beacons", async () => {
             const [room1] = makeRoomsWithStateEvents([alicesRoom1BeaconInfo]);
             const store = await makeOwnBeaconStore();
-            const beacon = room1.currentState.beacons.get(getBeaconInfoIdentifier(alicesRoom1BeaconInfo));
+            const beacon = room1.currentState.beacons.get(getBeaconInfoIdentifier(alicesRoom1BeaconInfo))!;
             const destroySpy = jest.spyOn(beacon, "destroy");
             // @ts-ignore
             store.onNotReady();
@@ -559,7 +559,7 @@ describe("OwnBeaconStore", () => {
 
             const [room1] = makeRoomsWithStateEvents([alicesRoom1BeaconInfo, alicesRoom2BeaconInfo]);
             const store = await makeOwnBeaconStore();
-            const room1BeaconInstance = store.beacons.get(getBeaconInfoIdentifier(alicesRoom1BeaconInfo));
+            const room1BeaconInstance = store.beacons.get(getBeaconInfoIdentifier(alicesRoom1BeaconInfo))!;
             const beaconDestroySpy = jest.spyOn(room1BeaconInstance, "destroy");
             const emitSpy = jest.spyOn(store, "emit");
 
@@ -610,7 +610,7 @@ describe("OwnBeaconStore", () => {
             expect(store.hasLiveBeacons()).toBe(true);
             const emitSpy = jest.spyOn(store, "emit");
 
-            const beacon = store.getBeaconById(getBeaconInfoIdentifier(alicesRoom1BeaconInfo));
+            const beacon = store.getBeaconById(getBeaconInfoIdentifier(alicesRoom1BeaconInfo))!;
 
             beacon.destroy();
             mockClient.emit(BeaconEvent.Destroy, beacon.identifier);
diff --git a/test/stores/SpaceStore-test.ts b/test/stores/SpaceStore-test.ts
index 1b9ae8da60..907d000a48 100644
--- a/test/stores/SpaceStore-test.ts
+++ b/test/stores/SpaceStore-test.ts
@@ -103,10 +103,11 @@ describe("SpaceStore", () => {
     const viewRoom = (roomId: string) => defaultDispatcher.dispatch({ action: Action.ViewRoom, room_id: roomId }, true);
 
     const run = async () => {
-        mocked(client).getRoom.mockImplementation((roomId) => rooms.find((room) => room.roomId === roomId));
-        mocked(client).getRoomUpgradeHistory.mockImplementation((roomId) => [
-            rooms.find((room) => room.roomId === roomId),
-        ]);
+        mocked(client).getRoom.mockImplementation((roomId) => rooms.find((room) => room.roomId === roomId) || null);
+        mocked(client).getRoomUpgradeHistory.mockImplementation((roomId) => {
+            const room = rooms.find((room) => room.roomId === roomId);
+            return room ? [room] : [];
+        });
         await testUtils.setupAsyncStoreWithClient(store, client);
         jest.runOnlyPendingTimers();
     };
@@ -312,10 +313,12 @@ describe("SpaceStore", () => {
                 mkSpace(space3, [invite2]);
                 mkSpace(space4, [room4, fav2, space2, space3]);
 
-                mocked(client).getRoom.mockImplementation((roomId) => rooms.find((room) => room.roomId === roomId));
+                mocked(client).getRoom.mockImplementation(
+                    (roomId) => rooms.find((room) => room.roomId === roomId) || null,
+                );
 
                 [fav1, fav2, fav3].forEach((roomId) => {
-                    client.getRoom(roomId).tags = {
+                    client.getRoom(roomId)!.tags = {
                         "m.favourite": {
                             order: 0.5,
                         },
@@ -323,20 +326,20 @@ describe("SpaceStore", () => {
                 });
 
                 [invite1, invite2].forEach((roomId) => {
-                    mocked(client.getRoom(roomId)).getMyMembership.mockReturnValue("invite");
+                    mocked(client.getRoom(roomId)!).getMyMembership.mockReturnValue("invite");
                 });
 
                 // have dmPartner1 be in space1 with you
                 const mySpace1Member = new RoomMember(space1, testUserId);
                 mySpace1Member.membership = "join";
-                (rooms.find((r) => r.roomId === space1).getMembers as jest.Mock).mockReturnValue([
+                (rooms.find((r) => r.roomId === space1)!.getMembers as jest.Mock).mockReturnValue([
                     mySpace1Member,
                     dm1Partner,
                 ]);
                 // have dmPartner2 be in space2 with you
                 const mySpace2Member = new RoomMember(space2, testUserId);
                 mySpace2Member.membership = "join";
-                (rooms.find((r) => r.roomId === space2).getMembers as jest.Mock).mockReturnValue([
+                (rooms.find((r) => r.roomId === space2)!.getMembers as jest.Mock).mockReturnValue([
                     mySpace2Member,
                     dm2Partner,
                 ]);
@@ -349,15 +352,15 @@ describe("SpaceStore", () => {
                         event: true,
                         type: EventType.SpaceParent,
                         room: room2,
-                        user: client.getUserId(),
+                        user: client.getUserId()!,
                         skey: space2,
                         content: { via: [], canonical: true },
                         ts: Date.now(),
                     }) as MatrixEvent,
                 ]);
-                mocked(cliRoom2.currentState).getStateEvents.mockImplementation(room2MockStateEvents);
+                mocked(cliRoom2!.currentState).getStateEvents.mockImplementation(room2MockStateEvents);
                 const cliSpace2 = client.getRoom(space2);
-                mocked(cliSpace2.currentState).maySendStateEvent.mockImplementation(
+                mocked(cliSpace2!.currentState).maySendStateEvent.mockImplementation(
                     (evType: string, userId: string) => {
                         if (evType === EventType.SpaceChild) {
                             return userId === client.getUserId();
@@ -368,13 +371,13 @@ describe("SpaceStore", () => {
 
                 // room 3 claims to be a child of space3 but is not due to invalid m.space.parent (permissions)
                 const cliRoom3 = client.getRoom(room3);
-                mocked(cliRoom3.currentState).getStateEvents.mockImplementation(
+                mocked(cliRoom3!.currentState).getStateEvents.mockImplementation(
                     testUtils.mockStateEventImplementation([
                         mkEvent({
                             event: true,
                             type: EventType.SpaceParent,
                             room: room3,
-                            user: client.getUserId(),
+                            user: client.getUserId()!,
                             skey: space3,
                             content: { via: [], canonical: true },
                             ts: Date.now(),
@@ -382,7 +385,7 @@ describe("SpaceStore", () => {
                     ]),
                 );
                 const cliSpace3 = client.getRoom(space3);
-                mocked(cliSpace3.currentState).maySendStateEvent.mockImplementation(
+                mocked(cliSpace3!.currentState).maySendStateEvent.mockImplementation(
                     (evType: string, userId: string) => {
                         if (evType === EventType.SpaceChild) {
                             return false;
@@ -813,7 +816,7 @@ describe("SpaceStore", () => {
                     content: { membership: "join" },
                     ts: Date.now(),
                 });
-                const spaceRoom = client.getRoom(spaceId);
+                const spaceRoom = client.getRoom(spaceId)!;
                 mocked(spaceRoom.currentState).getStateEvents.mockImplementation(
                     testUtils.mockStateEventImplementation([memberEvent]),
                 );
@@ -929,7 +932,7 @@ describe("SpaceStore", () => {
 
         it("switch to unknown space is a nop", async () => {
             expect(store.activeSpace).toBe(MetaSpace.Home);
-            const space = client.getRoom(room1); // not a space
+            const space = client.getRoom(room1)!; // not a space
             store.setActiveSpace(space.roomId);
             expect(fn).not.toHaveBeenCalledWith(UPDATE_SELECTED_SPACE, space.roomId);
             expect(store.activeSpace).toBe(MetaSpace.Home);
@@ -962,6 +965,7 @@ describe("SpaceStore", () => {
                     member.membership = "join";
                     return member;
                 }
+                return null;
             });
 
             client.emit(RoomStateEvent.Members, event, space.currentState, dm1Partner);
@@ -1088,7 +1092,7 @@ describe("SpaceStore", () => {
             mkSpace(space1, [room1, room2, room3]);
             mkSpace(space2, [room1, room2]);
 
-            const cliRoom2 = client.getRoom(room2);
+            const cliRoom2 = client.getRoom(room2)!;
             mocked(cliRoom2.currentState).getStateEvents.mockImplementation(
                 testUtils.mockStateEventImplementation([
                     mkEvent({
@@ -1267,8 +1271,9 @@ describe("SpaceStore", () => {
                 case dm1Partner.userId:
                     return rootSpaceFriend;
             }
+            return null;
         });
-        expect(SpaceStore.instance.getSpaceFilteredUserIds(space1).has(dm1Partner.userId)).toBeFalsy();
+        expect(SpaceStore.instance.getSpaceFilteredUserIds(space1)!.has(dm1Partner.userId)).toBeFalsy();
         const memberEvent = mkEvent({
             event: true,
             type: EventType.RoomMember,
@@ -1281,7 +1286,7 @@ describe("SpaceStore", () => {
         });
         client.emit(RoomStateEvent.Members, memberEvent, rootSpace.currentState, dm1Partner);
         jest.runOnlyPendingTimers();
-        expect(SpaceStore.instance.getSpaceFilteredUserIds(space1).has(dm1Partner.userId)).toBeTruthy();
+        expect(SpaceStore.instance.getSpaceFilteredUserIds(space1)!.has(dm1Partner.userId)).toBeTruthy();
         const dm1Room = mkRoom(dm1);
         dm1Room.getMyMembership.mockReturnValue("join");
         client.emit(ClientEvent.Room, dm1Room);
diff --git a/test/stores/room-list/SlidingRoomListStore-test.ts b/test/stores/room-list/SlidingRoomListStore-test.ts
index 3014423349..6d23e16698 100644
--- a/test/stores/room-list/SlidingRoomListStore-test.ts
+++ b/test/stores/room-list/SlidingRoomListStore-test.ts
@@ -198,10 +198,10 @@ describe("SlidingRoomListStore", () => {
             return keyToListData[key] || null;
         });
 
-        expect(store.getTagsForRoom(new Room(roomA, context.client!, context.client!.getUserId()))).toEqual([
+        expect(store.getTagsForRoom(new Room(roomA, context.client!, context.client!.getUserId()!))).toEqual([
             DefaultTagID.Untagged,
         ]);
-        expect(store.getTagsForRoom(new Room(roomB, context.client!, context.client!.getUserId()))).toEqual([
+        expect(store.getTagsForRoom(new Room(roomB, context.client!, context.client!.getUserId()!))).toEqual([
             DefaultTagID.Favourite,
             DefaultTagID.Untagged,
         ]);
@@ -221,9 +221,9 @@ describe("SlidingRoomListStore", () => {
             0: roomA,
         };
         const rooms = [
-            new Room(roomA, context.client!, context.client!.getUserId()),
-            new Room(roomB, context.client!, context.client!.getUserId()),
-            new Room(roomC, context.client!, context.client!.getUserId()),
+            new Room(roomA, context.client!, context.client!.getUserId()!),
+            new Room(roomB, context.client!, context.client!.getUserId()!),
+            new Room(roomC, context.client!, context.client!.getUserId()!),
         ];
         mocked(context.client!.getRoom).mockImplementation((roomId: string) => {
             switch (roomId) {
@@ -257,9 +257,9 @@ describe("SlidingRoomListStore", () => {
             2: roomIdC,
             0: roomIdA,
         };
-        const roomA = new Room(roomIdA, context.client!, context.client!.getUserId());
-        const roomB = new Room(roomIdB, context.client!, context.client!.getUserId());
-        const roomC = new Room(roomIdC, context.client!, context.client!.getUserId());
+        const roomA = new Room(roomIdA, context.client!, context.client!.getUserId()!);
+        const roomB = new Room(roomIdB, context.client!, context.client!.getUserId()!);
+        const roomC = new Room(roomIdC, context.client!, context.client!.getUserId()!);
         mocked(context.client!.getRoom).mockImplementation((roomId: string) => {
             switch (roomId) {
                 case roomIdA:
@@ -321,8 +321,8 @@ describe("SlidingRoomListStore", () => {
         const tagId = DefaultTagID.Favourite;
         const joinCount = 10;
         // seed the store with 2 rooms
-        const roomA = new Room(roomIdA, context.client!, context.client!.getUserId());
-        const roomC = new Room(roomIdC, context.client!, context.client!.getUserId());
+        const roomA = new Room(roomIdA, context.client!, context.client!.getUserId()!);
+        const roomC = new Room(roomIdC, context.client!, context.client!.getUserId()!);
         mocked(context.client!.getRoom).mockImplementation((roomId: string) => {
             switch (roomId) {
                 case roomIdA:
diff --git a/test/stores/room-list/SpaceWatcher-test.ts b/test/stores/room-list/SpaceWatcher-test.ts
index e8d43b66bd..c8a7c4f660 100644
--- a/test/stores/room-list/SpaceWatcher-test.ts
+++ b/test/stores/room-list/SpaceWatcher-test.ts
@@ -29,11 +29,13 @@ import { MatrixClientPeg } from "../../../src/MatrixClientPeg";
 import { SpaceFilterCondition } from "../../../src/stores/room-list/filters/SpaceFilterCondition";
 import DMRoomMap from "../../../src/utils/DMRoomMap";
 
-let filter: SpaceFilterCondition = null;
+let filter: SpaceFilterCondition | null = null;
 
 const mockRoomListStore = {
     addFilter: (f: SpaceFilterCondition) => (filter = f),
-    removeFilter: (): void => (filter = null),
+    removeFilter: (): void => {
+        filter = null;
+    },
 } as unknown as RoomListStoreClass;
 
 const getUserIdForRoomId = jest.fn();
@@ -74,7 +76,7 @@ describe("SpaceWatcher", () => {
             [MetaSpace.Orphans]: true,
         });
 
-        client.getRoom.mockImplementation((roomId) => rooms.find((room) => room.roomId === roomId));
+        client.getRoom.mockImplementation((roomId) => rooms.find((room) => room.roomId === roomId) || null);
         await setupAsyncStoreWithClient(store, client);
     });
 
@@ -99,7 +101,7 @@ describe("SpaceWatcher", () => {
         await setShowAllRooms(false);
 
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(MetaSpace.Home);
+        expect(filter!["space"]).toBe(MetaSpace.Home);
     });
 
     it("sets filter correctly for all -> space transition", async () => {
@@ -109,7 +111,7 @@ describe("SpaceWatcher", () => {
         SpaceStore.instance.setActiveSpace(space1);
 
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(space1);
+        expect(filter!["space"]).toBe(space1);
     });
 
     it("removes filter for home -> all transition", async () => {
@@ -128,7 +130,7 @@ describe("SpaceWatcher", () => {
         SpaceStore.instance.setActiveSpace(space1);
 
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(space1);
+        expect(filter!["space"]).toBe(space1);
     });
 
     it("removes filter for space -> all transition", async () => {
@@ -137,7 +139,7 @@ describe("SpaceWatcher", () => {
 
         SpaceStore.instance.setActiveSpace(space1);
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(space1);
+        expect(filter!["space"]).toBe(space1);
         SpaceStore.instance.setActiveSpace(MetaSpace.Home);
 
         expect(filter).toBeNull();
@@ -149,7 +151,7 @@ describe("SpaceWatcher", () => {
 
         SpaceStore.instance.setActiveSpace(MetaSpace.Favourites);
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(MetaSpace.Favourites);
+        expect(filter!["space"]).toBe(MetaSpace.Favourites);
         SpaceStore.instance.setActiveSpace(MetaSpace.Home);
 
         expect(filter).toBeNull();
@@ -161,7 +163,7 @@ describe("SpaceWatcher", () => {
 
         SpaceStore.instance.setActiveSpace(MetaSpace.People);
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(MetaSpace.People);
+        expect(filter!["space"]).toBe(MetaSpace.People);
         SpaceStore.instance.setActiveSpace(MetaSpace.Home);
 
         expect(filter).toBeNull();
@@ -173,7 +175,7 @@ describe("SpaceWatcher", () => {
 
         SpaceStore.instance.setActiveSpace(MetaSpace.Orphans);
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(MetaSpace.Orphans);
+        expect(filter!["space"]).toBe(MetaSpace.Orphans);
         SpaceStore.instance.setActiveSpace(MetaSpace.Home);
 
         expect(filter).toBeNull();
@@ -185,11 +187,11 @@ describe("SpaceWatcher", () => {
 
         new SpaceWatcher(mockRoomListStore);
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(space1);
+        expect(filter!["space"]).toBe(space1);
         SpaceStore.instance.setActiveSpace(MetaSpace.Home);
 
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(MetaSpace.Home);
+        expect(filter!["space"]).toBe(MetaSpace.Home);
     });
 
     it("updates filter correctly for space -> orphans transition", async () => {
@@ -198,11 +200,11 @@ describe("SpaceWatcher", () => {
 
         new SpaceWatcher(mockRoomListStore);
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(space1);
+        expect(filter!["space"]).toBe(space1);
         SpaceStore.instance.setActiveSpace(MetaSpace.Orphans);
 
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(MetaSpace.Orphans);
+        expect(filter!["space"]).toBe(MetaSpace.Orphans);
     });
 
     it("updates filter correctly for orphans -> people transition", async () => {
@@ -211,11 +213,11 @@ describe("SpaceWatcher", () => {
 
         new SpaceWatcher(mockRoomListStore);
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(MetaSpace.Orphans);
+        expect(filter!["space"]).toBe(MetaSpace.Orphans);
         SpaceStore.instance.setActiveSpace(MetaSpace.People);
 
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(MetaSpace.People);
+        expect(filter!["space"]).toBe(MetaSpace.People);
     });
 
     it("updates filter correctly for space -> space transition", async () => {
@@ -224,11 +226,11 @@ describe("SpaceWatcher", () => {
 
         new SpaceWatcher(mockRoomListStore);
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(space1);
+        expect(filter!["space"]).toBe(space1);
         SpaceStore.instance.setActiveSpace(space2);
 
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(space2);
+        expect(filter!["space"]).toBe(space2);
     });
 
     it("doesn't change filter when changing showAllRooms mode to true", async () => {
@@ -237,11 +239,11 @@ describe("SpaceWatcher", () => {
 
         new SpaceWatcher(mockRoomListStore);
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(space1);
+        expect(filter!["space"]).toBe(space1);
         await setShowAllRooms(true);
 
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(space1);
+        expect(filter!["space"]).toBe(space1);
     });
 
     it("doesn't change filter when changing showAllRooms mode to false", async () => {
@@ -250,10 +252,10 @@ describe("SpaceWatcher", () => {
 
         new SpaceWatcher(mockRoomListStore);
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(space1);
+        expect(filter!["space"]).toBe(space1);
         await setShowAllRooms(false);
 
         expect(filter).toBeInstanceOf(SpaceFilterCondition);
-        expect(filter["space"]).toBe(space1);
+        expect(filter!["space"]).toBe(space1);
     });
 });
diff --git a/test/stores/room-list/filters/VisibilityProvider-test.ts b/test/stores/room-list/filters/VisibilityProvider-test.ts
index e8f2781fec..80296c2bda 100644
--- a/test/stores/room-list/filters/VisibilityProvider-test.ts
+++ b/test/stores/room-list/filters/VisibilityProvider-test.ts
@@ -109,14 +109,14 @@ describe("VisibilityProvider", () => {
         });
 
         it("should return false if visibility customisation returns false", () => {
-            mocked(RoomListCustomisations.isRoomVisible).mockReturnValue(false);
+            mocked(RoomListCustomisations.isRoomVisible!).mockReturnValue(false);
             const room = createRoom();
             expect(VisibilityProvider.instance.isRoomVisible(room)).toBe(false);
             expect(RoomListCustomisations.isRoomVisible).toHaveBeenCalledWith(room);
         });
 
         it("should return true if visibility customisation returns true", () => {
-            mocked(RoomListCustomisations.isRoomVisible).mockReturnValue(true);
+            mocked(RoomListCustomisations.isRoomVisible!).mockReturnValue(true);
             const room = createRoom();
             expect(VisibilityProvider.instance.isRoomVisible(room)).toBe(true);
             expect(RoomListCustomisations.isRoomVisible).toHaveBeenCalledWith(room);
diff --git a/test/stores/widgets/StopGapWidget-test.ts b/test/stores/widgets/StopGapWidget-test.ts
index 66b7a25e35..38e9983d49 100644
--- a/test/stores/widgets/StopGapWidget-test.ts
+++ b/test/stores/widgets/StopGapWidget-test.ts
@@ -80,8 +80,8 @@ describe("StopGapWidget", () => {
         beforeEach(() => {
             voiceBroadcastInfoEvent = mkEvent({
                 event: true,
-                room: client.getRoom("x").roomId,
-                user: client.getUserId(),
+                room: client.getRoom("x")?.roomId,
+                user: client.getUserId()!,
                 type: VoiceBroadcastInfoEventType,
                 content: {},
             });
diff --git a/test/stores/widgets/WidgetPermissionStore-test.ts b/test/stores/widgets/WidgetPermissionStore-test.ts
index aa3af71f79..d9f1cbb804 100644
--- a/test/stores/widgets/WidgetPermissionStore-test.ts
+++ b/test/stores/widgets/WidgetPermissionStore-test.ts
@@ -59,22 +59,22 @@ describe("WidgetPermissionStore", () => {
     });
 
     it("should persist OIDCState.Allowed for a widget", () => {
-        widgetPermissionStore.setOIDCState(w, WidgetKind.Account, null, OIDCState.Allowed);
+        widgetPermissionStore.setOIDCState(w, WidgetKind.Account, roomId, OIDCState.Allowed);
         // check it remembered the value
-        expect(widgetPermissionStore.getOIDCState(w, WidgetKind.Account, null)).toEqual(OIDCState.Allowed);
+        expect(widgetPermissionStore.getOIDCState(w, WidgetKind.Account, roomId)).toEqual(OIDCState.Allowed);
     });
 
     it("should persist OIDCState.Denied for a widget", () => {
-        widgetPermissionStore.setOIDCState(w, WidgetKind.Account, null, OIDCState.Denied);
+        widgetPermissionStore.setOIDCState(w, WidgetKind.Account, roomId, OIDCState.Denied);
         // check it remembered the value
-        expect(widgetPermissionStore.getOIDCState(w, WidgetKind.Account, null)).toEqual(OIDCState.Denied);
+        expect(widgetPermissionStore.getOIDCState(w, WidgetKind.Account, roomId)).toEqual(OIDCState.Denied);
     });
 
     it("should update OIDCState for a widget", () => {
-        widgetPermissionStore.setOIDCState(w, WidgetKind.Account, null, OIDCState.Allowed);
-        widgetPermissionStore.setOIDCState(w, WidgetKind.Account, null, OIDCState.Denied);
+        widgetPermissionStore.setOIDCState(w, WidgetKind.Account, roomId, OIDCState.Allowed);
+        widgetPermissionStore.setOIDCState(w, WidgetKind.Account, roomId, OIDCState.Denied);
         // check it remembered the latest value
-        expect(widgetPermissionStore.getOIDCState(w, WidgetKind.Account, null)).toEqual(OIDCState.Denied);
+        expect(widgetPermissionStore.getOIDCState(w, WidgetKind.Account, roomId)).toEqual(OIDCState.Denied);
     });
 
     it("should scope the location for a widget when setting OIDC state", () => {
diff --git a/test/test-utils/beacon.ts b/test/test-utils/beacon.ts
index 0a388336a7..18ef73bdae 100644
--- a/test/test-utils/beacon.ts
+++ b/test/test-utils/beacon.ts
@@ -197,7 +197,7 @@ export const makeRoomWithBeacons = (
     locationEvents?: MatrixEvent[],
 ): Beacon[] => {
     const room = makeRoomWithStateEvents(beaconInfoEvents, { roomId, mockClient });
-    const beacons = beaconInfoEvents.map((event) => room.currentState.beacons.get(getBeaconInfoIdentifier(event)));
+    const beacons = beaconInfoEvents.map((event) => room.currentState.beacons.get(getBeaconInfoIdentifier(event))!);
     if (locationEvents) {
         beacons.forEach((beacon) => {
             // this filtering happens in roomState, which is bypassed here
diff --git a/test/test-utils/composer.ts b/test/test-utils/composer.ts
index 80cc9f0470..85227acbc1 100644
--- a/test/test-utils/composer.ts
+++ b/test/test-utils/composer.ts
@@ -31,7 +31,7 @@ export const addTextToComposer = (container: HTMLElement, text: string) =>
                 getData: (type: string) => (type === "text/plain" ? text : undefined),
             } as unknown as DataTransfer,
         };
-        fireEvent.paste(container.querySelector('[role="textbox"]'), pasteEvent);
+        fireEvent.paste(container.querySelector('[role="textbox"]')!, pasteEvent);
     });
 
 export const addTextToComposerEnzyme = (wrapper: ReactWrapper, text: string) =>
diff --git a/test/test-utils/utilities.ts b/test/test-utils/utilities.ts
index e2acc904e3..a03e10b83e 100644
--- a/test/test-utils/utilities.ts
+++ b/test/test-utils/utilities.ts
@@ -37,7 +37,7 @@ export function untilDispatch(
     dispatcher = defaultDispatcher,
     timeout = 1000,
 ): Promise<ActionPayload> {
-    const callerLine = new Error().stack.toString().split("\n")[2];
+    const callerLine = new Error().stack!.toString().split("\n")[2];
     if (typeof waitForAction === "string") {
         const action = waitForAction;
         waitForAction = (payload) => {
@@ -89,10 +89,10 @@ export function untilDispatch(
 export function untilEmission(
     emitter: EventEmitter,
     eventName: string,
-    check: (...args: any[]) => boolean = undefined,
+    check?: (...args: any[]) => boolean,
     timeout = 1000,
 ): Promise<void> {
-    const callerLine = new Error().stack.toString().split("\n")[2];
+    const callerLine = new Error().stack!.toString().split("\n")[2];
     return new Promise((resolve, reject) => {
         let fulfilled = false;
         let timeoutId: number;
diff --git a/test/theme-test.ts b/test/theme-test.ts
index 0298cd48c8..d1dc5f68cc 100644
--- a/test/theme-test.ts
+++ b/test/theme-test.ts
@@ -58,7 +58,7 @@ describe("theme", () => {
             // When
             await new Promise((resolve) => {
                 setTheme("light").then(resolve);
-                lightTheme.onload(void 0);
+                lightTheme.onload!({} as Event);
             });
 
             // Then
@@ -72,7 +72,7 @@ describe("theme", () => {
             return expect(
                 new Promise((resolve) => {
                     setTheme("light").catch((e) => resolve(e));
-                    lightTheme.onerror("call onerror");
+                    lightTheme.onerror!("call onerror");
                 }),
             ).resolves.toBe("call onerror");
         });
diff --git a/test/useTopic-test.tsx b/test/useTopic-test.tsx
index 5cab29e9b6..2f7e0ac757 100644
--- a/test/useTopic-test.tsx
+++ b/test/useTopic-test.tsx
@@ -42,7 +42,7 @@ describe("useTopic", () => {
 
         function RoomTopic() {
             const topic = useTopic(room);
-            return <p>{topic.text}</p>;
+            return <p>{topic!.text}</p>;
         }
 
         render(<RoomTopic />);
diff --git a/test/utils/MegolmExportEncryption-test.ts b/test/utils/MegolmExportEncryption-test.ts
index 4e22c7aec4..69d803073f 100644
--- a/test/utils/MegolmExportEncryption-test.ts
+++ b/test/utils/MegolmExportEncryption-test.ts
@@ -85,10 +85,6 @@ describe("MegolmExportEncryption", function () {
         MegolmExportEncryption = require("../../src/utils/MegolmExportEncryption");
     });
 
-    afterAll(() => {
-        window.crypto = undefined;
-    });
-
     describe("decrypt", function () {
         it("should handle missing header", function () {
             const input = stringToArray(`-----`);
diff --git a/test/utils/beacon/geolocation-test.ts b/test/utils/beacon/geolocation-test.ts
index 0f9aba483f..c3407a01f5 100644
--- a/test/utils/beacon/geolocation-test.ts
+++ b/test/utils/beacon/geolocation-test.ts
@@ -62,8 +62,6 @@ describe("geolocation utilities", () => {
             const pos: GenericPosition = {
                 latitude: 43.2,
                 longitude: 12.4,
-                altitude: null,
-                accuracy: null,
 
                 timestamp: 12334,
             };
diff --git a/test/utils/export-test.tsx b/test/utils/export-test.tsx
index 95d4799d31..a75af856db 100644
--- a/test/utils/export-test.tsx
+++ b/test/utils/export-test.tsx
@@ -45,6 +45,8 @@ interface ITestContent extends IContent {
 }
 
 describe("export", function () {
+    const setProgressText = jest.fn();
+
     let mockExportOptions: IExportOptions;
     let mockRoom: Room;
     let ts0: number;
@@ -63,7 +65,7 @@ describe("export", function () {
         };
 
         function createRoom() {
-            const room = new Room(generateRoomId(), null, client.getUserId());
+            const room = new Room(generateRoomId(), client, client.getUserId()!);
             return room;
         }
         mockRoom = createRoom();
@@ -146,7 +148,7 @@ describe("export", function () {
     }
 
     function mkEvents() {
-        const matrixEvents = [];
+        const matrixEvents: MatrixEvent[] = [];
         let i: number;
         // plain text
         for (i = 0; i < 10; i++) {
@@ -237,7 +239,7 @@ describe("export", function () {
     });
 
     it("checks if the icons' html corresponds to export regex", function () {
-        const exporter = new HTMLExporter(mockRoom, ExportType.Beginning, mockExportOptions, null);
+        const exporter = new HTMLExporter(mockRoom, ExportType.Beginning, mockExportOptions, setProgressText);
         const fileRegex = /<span class="mx_MFileBody_info_icon">.*?<\/span>/;
         expect(fileRegex.test(renderToString(exporter.getEventTile(mkFileEvent(), true)))).toBeTruthy();
     });
@@ -251,7 +253,7 @@ describe("export", function () {
                 maxSize: 100 * 1024 * 1024,
                 attachmentsIncluded: true,
             },
-            null,
+            setProgressText,
         );
         const imageRegex = /<img.+ src="mxc:\/\/test.org" alt="image.png"\/>/;
         expect(imageRegex.test(renderToString(exporter.getEventTile(mkImageEvent(), true)))).toBeTruthy();
@@ -284,13 +286,13 @@ describe("export", function () {
         ],
     ];
     it.each(invalidExportOptions)("%s", (_d, options) => {
-        expect(() => new PlainTextExporter(mockRoom, ExportType.Beginning, options, null)).toThrowError(
+        expect(() => new PlainTextExporter(mockRoom, ExportType.Beginning, options, setProgressText)).toThrowError(
             "Invalid export options",
         );
     });
 
     it("tests the file extension splitter", function () {
-        const exporter = new PlainTextExporter(mockRoom, ExportType.Beginning, mockExportOptions, null);
+        const exporter = new PlainTextExporter(mockRoom, ExportType.Beginning, mockExportOptions, setProgressText);
         const fileNameWithExtensions: Record<string, [string, string]> = {
             "": ["", ""],
             "name": ["name", ""],
@@ -327,14 +329,14 @@ describe("export", function () {
                 expectedText: '<@me:here "This"> Reply',
             },
         ];
-        const exporter = new PlainTextExporter(mockRoom, ExportType.Beginning, mockExportOptions, null);
+        const exporter = new PlainTextExporter(mockRoom, ExportType.Beginning, mockExportOptions, setProgressText);
         for (const content of eventContents) {
             expect(exporter.textForReplyEvent(content)).toBe(content.expectedText);
         }
     });
 
     it("checks if the render to string doesn't throw any error for different types of events", function () {
-        const exporter = new HTMLExporter(mockRoom, ExportType.Beginning, mockExportOptions, null);
+        const exporter = new HTMLExporter(mockRoom, ExportType.Beginning, mockExportOptions, setProgressText);
         for (const event of events) {
             expect(renderToString(exporter.getEventTile(event, false))).toBeTruthy();
         }
diff --git a/test/voice-broadcast/audio/VoiceBroadcastRecorder-test.ts b/test/voice-broadcast/audio/VoiceBroadcastRecorder-test.ts
index b2a0e7da50..7d47918b1f 100644
--- a/test/voice-broadcast/audio/VoiceBroadcastRecorder-test.ts
+++ b/test/voice-broadcast/audio/VoiceBroadcastRecorder-test.ts
@@ -83,15 +83,15 @@ describe("VoiceBroadcastRecorder", () => {
 
         const simulateFirstChunk = (): void => {
             // send headers in wrong order and multiple times to test robustness for that
-            voiceRecording.onDataAvailable(headers2);
-            voiceRecording.onDataAvailable(headers1);
-            voiceRecording.onDataAvailable(headers1);
-            voiceRecording.onDataAvailable(headers2);
+            voiceRecording.onDataAvailable!(headers2);
+            voiceRecording.onDataAvailable!(headers1);
+            voiceRecording.onDataAvailable!(headers1);
+            voiceRecording.onDataAvailable!(headers2);
             // set recorder seconds to something greater than the test chunk length of 30
             // @ts-ignore
             voiceRecording.recorderSeconds = 42;
-            voiceRecording.onDataAvailable(chunk1);
-            voiceRecording.onDataAvailable(headers1);
+            voiceRecording.onDataAvailable!(chunk1);
+            voiceRecording.onDataAvailable!(headers1);
         };
 
         const expectOnFirstChunkRecorded = (): void => {
@@ -164,7 +164,7 @@ describe("VoiceBroadcastRecorder", () => {
 
         describe("when the first header from recorder has been received", () => {
             beforeEach(() => {
-                voiceRecording.onDataAvailable(headers1);
+                voiceRecording.onDataAvailable!(headers1);
             });
 
             itShouldNotEmitAChunkRecordedEvent();
@@ -172,8 +172,8 @@ describe("VoiceBroadcastRecorder", () => {
 
         describe("when the second header from recorder has been received", () => {
             beforeEach(() => {
-                voiceRecording.onDataAvailable(headers1);
-                voiceRecording.onDataAvailable(headers2);
+                voiceRecording.onDataAvailable!(headers1);
+                voiceRecording.onDataAvailable!(headers2);
             });
 
             itShouldNotEmitAChunkRecordedEvent();
@@ -181,9 +181,9 @@ describe("VoiceBroadcastRecorder", () => {
 
         describe("when a third page from recorder has been received", () => {
             beforeEach(() => {
-                voiceRecording.onDataAvailable(headers1);
-                voiceRecording.onDataAvailable(headers2);
-                voiceRecording.onDataAvailable(chunk1);
+                voiceRecording.onDataAvailable!(headers1);
+                voiceRecording.onDataAvailable!(headers2);
+                voiceRecording.onDataAvailable!(chunk1);
             });
 
             itShouldNotEmitAChunkRecordedEvent();
@@ -235,15 +235,15 @@ describe("VoiceBroadcastRecorder", () => {
                 simulateFirstChunk();
 
                 // simulate a second chunk
-                voiceRecording.onDataAvailable(chunk2a);
+                voiceRecording.onDataAvailable!(chunk2a);
 
                 // send headers again to test robustness for that
-                voiceRecording.onDataAvailable(headers2);
+                voiceRecording.onDataAvailable!(headers2);
 
                 // add another 30 seconds for the next chunk
                 // @ts-ignore
                 voiceRecording.recorderSeconds = 72;
-                voiceRecording.onDataAvailable(chunk2b);
+                voiceRecording.onDataAvailable!(chunk2b);
             });
 
             it("should emit ChunkRecorded events", () => {