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/auth/SetupEncryptionBody.tsx

@@ -141,7 +141,7 @@ export default class SetupEncryptionBody extends React.Component<IProps, IState>
         this.props.onFinished();
     };
 
-    public render(): JSX.Element {
+    public render(): React.ReactNode {
         const { phase, lostKeys } = this.state;
 
         if (this.state.verificationRequest) {