main_common.dart

void main_common() async {
  //...
  runZoned<Future<Null>>(() async {
    runApp(CrashyApp());
  }, onError: (error, stackTrace) async {
	  // Since the state can be null, we use `?.` to verify if it is null. If it is null, we don't do anything, if it is NOT null, we call the `push` function on it
    navigatorKey.currentState?.push(
      MaterialPageRoute(builder: (_) => ErrorWidget(),
    ));
  });
}