The getter was called on null but the widgets still builds fine - flutter

Question

I'm trying to implement Provider instead of using State so after reading some tutorials, that are little hard to me to understand, because I didn't find something clear to say: "You're going to use Firebase, then here you should use ChangeNotifierProvider or Provider or StreamProvider etc."
So I found a tutorial by Jeff Delaney at Fireship that I tried to apply to my use case, but despite it works I'm not sure I did it properly, mostly because I get this message saying "The getter was called on null". I can suppress it by putting an "?" like user?.name but I want to understand what is going on and why despite the error the code still works fine.
Here's the code I have:
First I have a normal User model that works just fine creating model and returning name, tlf and other stuff from Firebase. This part is ok.
Then I have this database service from the Jeff's code:
class DatabaseService {
final Firestore _db = Firestore.instance;
/// Get a stream of a single document
Stream<User> streamUser (String id) {
return _db
.collection('profiles')
.document(id)
.snapshots()
.map((snap) => User.fromMap(snap.data));
}
}
Then I have the screen where I implemented the Provider:
class GestorScreen extends StatelessWidget {
final db = DatabaseService();
final FirebaseUser firebaseUser;
GestorScreen({Key key, #required this.firebaseUser});
#override
Widget build(BuildContext context) {
return StreamProvider<User>.value(
value: db.streamUser(firebaseUser.uid),
child: DashboardButtons(),
);
}
}
And the DashboardButtons class:
class DashboardButtons extends StatelessWidget {
#override
Widget build(BuildContext context) {
var user = Provider.of<User>(context);
return Scaffold(
appBar: AppBar(),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
user?.updated != null ? _button(CustomColors.emerald, () {
Navigator.push(context,
MaterialPageRoute(builder: (context) =>
Dashboard(user: user)));
}, 'Gestionar Perfil') : _button(CustomColors.emerald, () {
Navigator.push(context,
MaterialPageRoute(builder: (context) =>
UserAlta(user: user,)));
}, ' Dar de Alta (ßeta)'),
SizedBox(height: SizeConfig.blockSizeHorizontal * 7,),
.................
.................
.................
],
)
),
backgroundColor: CustomColors.newCreme,
)
}
}
The code works fine but if delete the "?" from user.updated it says that The getter 'updated' was called on null... still it works fine.
Can someone help me with this? Where is the problem with the getter? And did I implemented the Provider the right way?

Answer 1

Get the error when the user is null.
user?.updated is equal to user == null ? null : user.updated

Answer 2

its a safe navigation operator, when the user object is null, the whole expression returns null. Otherwise updated() method is run.
safe navigation operator