Flutter "null check operator used on a null value" while using routes in MaterialApp

Question

My main.dart file

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(App());
}

class App extends StatefulWidget {
  const App({super.key});

  @override
  State<App> createState() => _AppState();
}

class _AppState extends State<App> {
  final Future<FirebaseApp> _initialization = Firebase.initializeApp();

  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      // Initialize FlutterFire:
      future: _initialization,
      builder: (context, snapshot) {
        // Check for errors
        if (snapshot.hasError) {
          // ... show error page ...
          // → this does work
        }

        // Once complete, show your application
        if (snapshot.connectionState == ConnectionState.done) {

// my problem is somewhere inside this MaterialApp

          return MaterialApp(
            initialRoute: Navigator.defaultRouteName, // equals to '/'
            routes: appRoutes,
          );
        }

        // Otherwise, show something whilst waiting for initialization to complete
        // ... show loading page ...
        // → this does work
      },
    );
  }
}

---

my routes(appRoutes) definition (imported from another file)

var appRoutes = {
  Navigator.defaultRouteName: (context) => HomeScreen(),
  '/login': (context) => LoginScreen(),
  '/about': (context) =>  AboutScreen(),
  '/profile': (context) =>  ProfileScreen(),
  '/topics': (context) =>  TopicsScreen(),
};

---

As long as I just return a simple MaterialApp with some content, it does work fine. But the moment I add the routes -keyword (instead of the content) there is the null check operator error.

I did find this post, where there was a very similar problem but the solution didn't work for me: Flutter: MaterialApp throws Null check operator used error

The pages are very simple MaterialApps or Scaffolds just showing a Text

As an example: my HomeScreen() build widget

Widget build(BuildContext context) {
  return MaterialApp( // replacing this with a Scaffold didn't solve my problem either
    home: Container(
      child: Text(
        'This works',
        style: TextStyle(fontSize: 30,),
      ),
    ),
  );
}

---

I have a few outdated transitive dependencies (but flutter pub upgrade doesn't change anything - due to dependency constraints)

transitive dependencies: 
async                     *2.8.2    *2.8.2      *2.8.2      2.9.0    
characters                *1.2.0    *1.2.0      *1.2.0      1.2.1    
clock                     *1.1.0    *1.1.0      *1.1.0      1.1.1    
fake_async                *1.3.0    *1.3.0      *1.3.0      1.3.1    
matcher                   *0.12.11  *0.12.11    *0.12.11    0.12.12  
material_color_utilities  *0.1.4    *0.1.4      *0.1.4      0.1.5    
meta                      *1.7.0    *1.7.0      *1.7.0      1.8.0    
path                      *1.8.1    *1.8.1      *1.8.1      1.8.2    
source_span               *1.8.2    *1.8.2      *1.8.2      1.9.1    
string_scanner            *1.1.0    *1.1.0      *1.1.0      1.1.1    
term_glyph                *1.2.0    *1.2.0      *1.2.0      1.2.1    
test_api                  *0.4.9    *0.4.9      *0.4.9      0.4.12

My previous research suggests that the problem is caused by the routes. What am I doing wrong?

---

EDIT: Maybe it does matter, that I have connected my phone via USB to test the app. (Emulator is eating up too much RAM)

---

EDIT: I now modified the code, so that Linux and Web builds are also able to test the routes.

Same problem here.

Answer 1

Have you tried removing the futurebuilder just to initialize the firebase?

You can initialize it in the main function itself as an async function

 void main() async { WidgetsFlutterBinding.ensureInitialized(); await Firebase.initializeApp(); runApp(App()); } class App extends StatefulWidget { const App({super.key}); @override State<App> createState() => _AppState(); } class _AppState extends State<App> { @override Widget build(BuildContext context) { return MaterialApp( initialRoute: Navigator.defaultRouteName, // equals to '/' routes: appRoutes, ); } }