How to make me Signout in Flutter - flutter

Question

I am creating a Login , Logout Page in flutter when i use Stream and Provider . I get Some Errors.
Help me out of this
in the main.dart when i use the StreamProvider it says the intial data cannot be null, according to my Tutorial there is no intialdata and in auth.dart when i use the authStatchanges().map it gives me 'The argument type 'Userid Function(User)' can't be assigned to the parameter type 'Userid Function(User?)'
Error Places - auth change user stream & and StreamProvider in main.dart
Thanks
Auth.dart
import 'package:firebase_auth/firebase_auth.dart';
import 'package:wasthu/Services/user.dart';
class AuthService {
final FirebaseAuth _auth = FirebaseAuth.instance;
//create userobject based on firebase user
Userid? _userFromFirebaseUser(User user) {
return user != null ? Userid(uid: user.uid) : null;
}
// auth change user stream
Stream<Userid> get user {
return _auth
.authStateChanges()
.map((User user) => _userFromFirebaseUser(user));
}
//sign in anon
Future signInAnon() async {
try {
UserCredential result = await _auth.signInAnonymously();
User? user = result.user;
return _userFromFirebaseUser(user!);
} catch (e) {
print(e.toString());
return null;
}
}
//signout
Future signOut() async {
try {
return await _auth.signOut();
} catch (e) {
print(e.toString());
return null;
}
}
}
main.dart
import 'package:firebase_core/firebase_core.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:wasthu/Screens/Home/wrapper.dart';
import 'package:wasthu/Services/auth.dart';
import 'package:wasthu/Services/user.dart';
void main() async {
WidgetsFlutterBinding.ensureInitialized();
await Firebase.initializeApp();
runApp(MaterialApp(
home: MyApp(),
debugShowCheckedModeBanner: false,
));
}
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return StreamProvider<Userid>.value(
value: AuthService().user,
initialData: null,
child: MaterialApp(
home: Wrapper(),
),
);
}
}
user.dart
class Userid {
final String uid;
Userid({required this.uid});
}