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/structures/MatrixChat.tsx

@@ -2021,7 +2021,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         return fragmentAfterLogin;
     }
 
-    public render(): JSX.Element {
+    public render(): React.ReactNode {
         const fragmentAfterLogin = this.getFragmentAfterLogin();
         let view = null;