options != null FirebaseOptions cannot be null when creating the default app.

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp(
    // Replace with actual values
    options: FirebaseOptions(
      apiKey: "XXX",
      appId: "XXX",
      messagingSenderId: "XXX",
      projectId: "XXX",
    ),
  );
  runApp(MyApp());
}