Flutter Firebase Authentication: Signout gives the error An exception was throw by _MapStream<User?, UserObject?> listened by

I was following TheNetNinja's tutorial on YouTube : (https://www.youtube.com/watch?v=v3sY3RWciNw&list=PL4cUxeGkcC9j--TKIdkb3ISfRbJeJYQwC&index=9), When I try to sign out, It gives the exception:

An exception was throw by _MapStream<User?, UserObject?> listened by StreamProvider<UserObject?>, but no catchError was provided.

I've read all the solutions on the net, but couldn't find one that fits. Since the video is from Oct 2019, I had to upgrade some parts of the code. I'll be very grateful If someone helps...

Here's AuthService class:

  final FirebaseAuth _auth = FirebaseAuth.instance;

  //create user obj based on Firebase user
  UserObject? _userObjectFromFirebaseUser(User user) {
    return user != null ? UserObject(uid: user.uid) : null;
  }

  //auth change user stream
  Stream<UserObject?> get user {
    return _auth
        .authStateChanges()
        .map((User? user) => _userObjectFromFirebaseUser(user!));
  }
  //sign in anon
  Future signInAnon() async {
    try {
      UserCredential result = await _auth.signInAnonymously();
      User? user = result.user;
      return _userObjectFromFirebaseUser(user!);
    } catch (e) {
      print(e.toString());
      return null;
    }
  }
  //sign in with email and password

  //register with email and password

  //sign out
  Future signOut() async {
    try {
      return await _auth.signOut();
    } catch (e) {
      print(e.toString());
      return null;
    }
  }
}

User object class:

class UserObject {
  final String uid;

  UserObject({required this.uid});
}

main:

class MyApp extends StatelessWidget {
  final Future<FirebaseApp> _fbapp = Firebase.initializeApp();
  MyApp({Key? key}) : super(key: key);

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return StreamProvider<UserObject?>.value(
        initialData: null,
        value: AuthService().user,
        child: MaterialApp(
          home: Wrapper(),
        ));
  }
}

Wrapper:

class Wrapper extends StatelessWidget {
  const Wrapper({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final user = Provider.of<UserObject?>(context);

    if (user == null) {
      return Authenticate();
    } else {
      return HomeScreen();
    }
  }
}