Question related to custom User Model

I want to add more fields to User model, for example, name, sex, job title, age, etc. Here is my code:
```
Stream get user {
// return _auth.onAuthStateChanged.map(_fromFirebaseUser);

final theUser = _auth.onAuthStateChanged.map((firebaseUser) {
final result = Firestore.instance.collection("users")
.document(firebaseUser.uid).snapshots().map((snapshot) {
return User(
uid: user.uid,
name: snapshot.data['name'],
email: user.email,
age: snapshot.data['age'],
gender: snapshot.data['gender']
);
}
return result;
});
return theUser;
}
```

The basic idea is I will get the data from users collection and populate the User model. But I got the following error message:

> The argument type 'Stream>' can't be assigned to the parameter type 'Stream'.

Need your advice. Thanks.