Conform more of the codebase to strictNullChecks (#10350

* Conform more of the codebase to `strictNullChecks`

* Iterate

* Generics ftw

* Iterate

src/components/structures/auth/header/AuthHeaderDisplay.tsx

@@ -27,7 +27,7 @@ interface Props {
 export function AuthHeaderDisplay({ title, icon, serverPicker, children }: PropsWithChildren<Props>): JSX.Element {
     const context = useContext(AuthHeaderContext);
     if (!context) {
-        return null;
+        return <></>;
     }
     const current = context.state.length ? context.state[0] : null;
     return (