Bloc Library Null - flutter

Question

In appbar I am trying to show profile icon after logged. When app start, appbar show profile icon, but at the same time in debug console give me an error 'A build function returned null'. When open profile page and return back, still the same error 'returned null' How to solve it?
class TestApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MultiBlocProvider(
providers: [
BlocProvider(
create: (context) => AuthBloc(
authService: AuthService())
..add(
AppStart(),
),
),
],
child: MaterialApp(
home: HomePage(),
),
);
}
}
homepage:
class HomePage extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
actions: <Widget>[
BlocBuilder<AuthBloc, AuthState>(
builder: (context, state) {
if (state is Authenticated) {
return profileIcon(context);
} else if (state is UnAuthenticated) {
return logIn(context);
}
},
),
],
),
);
}
}
bloc
#override
AuthState get initialState => AuthState();
#override
Stream<AuthState> mapEventToState(AuthEvent event) async* {
if (event is AppStart) {
try {
final user = await AuthService.getCurrentUser();
yield Authenticated(user: user);
} catch (e) {
yield UnAuthenticated();
}
}
}
icon:
Widget profileIcon(context) {
return Row(
children: <Widget>[
FlatButton.icon(
icon: Icon(),
label: Text(
'Profile',
),
onPressed: () {
Navigator.push(context,
MaterialPageRoute(builder: (context) => UserProfile()));
},
),
],
);
}
state:
class Authenticated extends AuthState {
final FirebaseUser user;
Authenticated({this.user});
#override
List<Object> get props => [user];
}
class UnAuthenticated extends AuthState {
#override
List<Object> get props => [];
}

Answer 1

I'm not really sure but my guess is you have another state for your initialState which is not handled in the BlocBuilder. Even though you add AppStart event right after providing AuthBloc which will end up with either Authenticated or UnAuthenticated state, you still need to put another else for your initialState. Even if it's not the case, try to add an else statement
appBar: AppBar(
actions: <Widget>[
BlocBuilder<AuthBloc, AuthState>(
builder: (context, state) {
if (state is Authenticated) {
return profileIcon(context);
} else if (state is UnAuthenticated) {
return logIn(context);
} else {
return Container();
}
},
),
],
),