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

src/components/views/emojipicker/Category.tsx

@@ -69,7 +69,7 @@ class Category extends React.PureComponent<IProps> {
         );
     };
 
-    public render(): JSX.Element {
+    public render(): React.ReactNode {
         const { emojis, name, heightBefore, viewportHeight, scrollTop } = this.props;
         if (!emojis || emojis.length === 0) {
             return null;

src/components/views/emojipicker/Emoji.tsx

@@ -30,7 +30,7 @@ interface IProps {
 }
 
 class Emoji extends React.PureComponent<IProps> {
-    public render(): JSX.Element {
+    public render(): React.ReactNode {
         const { onClick, onMouseEnter, onMouseLeave, emoji, selectedEmojis } = this.props;
         const isSelected = selectedEmojis && selectedEmojis.has(emoji.unicode);
         return (

src/components/views/emojipicker/EmojiPicker.tsx

@@ -249,7 +249,7 @@ class EmojiPicker extends React.Component<IProps, IState> {
         return CATEGORY_HEADER_HEIGHT + Math.ceil(count / EMOJIS_PER_ROW) * EMOJI_HEIGHT;
     }
 
-    public render(): JSX.Element {
+    public render(): React.ReactNode {
         let heightBefore = 0;
         return (
             <div className="mx_EmojiPicker" data-testid="mx_EmojiPicker">

src/components/views/emojipicker/Header.tsx

@@ -82,7 +82,7 @@ class Header extends React.PureComponent<IProps> {
         }
     };
 
-    public render(): JSX.Element {
+    public render(): React.ReactNode {
         return (
             <nav
                 className="mx_EmojiPicker_header"

src/components/views/emojipicker/Preview.tsx

@@ -24,7 +24,7 @@ interface IProps {
 }
 
 class Preview extends React.PureComponent<IProps> {
-    public render(): JSX.Element {
+    public render(): React.ReactNode {
         const {
             unicode,
             label,

src/components/views/emojipicker/QuickReactions.tsx

@@ -59,7 +59,7 @@ class QuickReactions extends React.Component<IProps, IState> {
         });
     };
 
-    public render(): JSX.Element {
+    public render(): React.ReactNode {
         return (
             <section className="mx_EmojiPicker_footer mx_EmojiPicker_quick mx_EmojiPicker_category">
                 <h2 className="mx_EmojiPicker_quick_header mx_EmojiPicker_category_label">

src/components/views/emojipicker/ReactionPicker.tsx

@@ -130,7 +130,7 @@ class ReactionPicker extends React.Component<IProps, IState> {
         return true;
     };
 
-    public render(): JSX.Element {
+    public render(): React.ReactNode {
         return (
             <EmojiPicker
                 onChoose={this.onChoose}

src/components/views/emojipicker/Search.tsx

@@ -46,7 +46,7 @@ class Search extends React.PureComponent<IProps> {
         }
     };
 
-    public render(): JSX.Element {
+    public render(): React.ReactNode {
         let rightButton;
         if (this.props.query) {
             rightButton = (