Conform more of the code base to strict null checking (#10147)

* Conform more of the code base to strict null checking

* More strict fixes

* More strict work

* Fix missing optional type

* Iterate

test/voice-broadcast/stores/VoiceBroadcastRecordingsStore-test.ts

@@ -44,6 +44,7 @@ describe("VoiceBroadcastRecordingsStore", () => {
             if (roomId === room.roomId) {
                 return room;
             }
+            return null;
         });
         infoEvent = mkVoiceBroadcastInfoStateEvent(
             roomId,