The getter 'uid' was called on null. Receiver: null Tried calling: uid - firebase

Question

this error "
"The getter 'uid' was called on null.Receiver: nullTried calling: uid"
I Faced when i try to sign out from any screen "except home screen" ,
is there any solution for this problem ??
Wrapper :
class Wrapper extends StatelessWidget {
#override
Widget build(BuildContext context) {
final user = Provider.of<User_fb>(context);
// return home or login
if (user == null) {
return Login();
} else {
print(user.uid);
return Home();
}
}
}
auth :
Future Signinwithemailandpassword(var Res_email,var Res_Password) async{
try{
UserCredential result= await _auth.signInWithEmailAndPassword(email: Res_email, password: Res_Password);
User user = result.user;
return _userfromfirebase(user);
}catch(e){
return null;
}
}
Future signOut () async{
try{
return await _auth.signOut();
}
catch(e){
print(e.toString());
print("error at signOut ");
return null;
}
}
main :
void main() async {
WidgetsFlutterBinding.ensureInitialized();
await Firebase.initializeApp();
runApp(Main());
}
class Main extends StatefulWidget {
#override
_MainState createState() => _MainState();
}
class _MainState extends State<Main> {
#override
Widget build(BuildContext context) {
return StreamProvider<User_fb>.value(
value: Authservice().user,
child: MaterialApp(
debugShowCheckedModeBanner: false,
theme: ThemeData(
primaryColor: Color.fromRGBO(255, 255, 255, 1),
shadowColor: Colors.transparent,
highlightColor: Colors.transparent),
home: Wrapper(),
),
);
}
}
Sign-out button :
ListTile(
leading: Icon(Ionicons.log_out_outline,
color: Color.fromRGBO(86, 197, 150, 1)),
title: Text('Log out'),
onTap: () async {
await _auth.signOut();
},
),
console :
======== Exception caught by widgets library =======================================================
The following NoSuchMethodError was thrown building Br(dirty, dependencies: [_InheritedProviderScope<User_fb>], state: _QrState#24e19):
The getter 'uid' was called on null.
Receiver: null
Tried calling: uid
The relevant error-causing widget was:
Qr file:///G:/AndroidStudioProjects/facem/lib/Screens/Home/Home.dart:687:67
When the exception was thrown, this was the stack:
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
#1 _QrState.build (package:my_compound/Screens/Qr/qr.dart:99:45)
#2 StatefulElement.build (package:flutter/src/widgets/framework.dart:4691:27)
#3 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4574:15)
#4 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4746:11)
...

Answer 1

this happens because user is null, So use null check operator.
something like this user?.uid or user.uid ?? '',
TIP: Alway use dart null safety when using flutter.