Multi-Provider invalid member on null: 'collection' on provider construct - firebase

Question

The error received:
NoSuchMethodError: invalid member on null: 'collection'
I'm using the Flutter Provider Package 4.3.2+2 for complex state management.
I get my data from Firebase, this is the data structure:
This is the provider class:
class ClientsProvider extends ChangeNotifier {
FirebaseFirestore _fs;
StreamSubscription<QuerySnapshot> _stream;
List<QueryDocumentSnapshot> clients = [];
ClientsProvider() {
_stream = _fs.collection("clients").snapshots().listen((event) {//THIS IS WHERE THE ERROR POINTS
clients = event.docs;
notifyListeners();
});
}
#override
void dispose() {
super.dispose();
_stream.cancel();
}
}
This is the parent widget:
class _ParentState extends State<Parent> {
#override
Widget build(BuildContext context) {
return MultiProvider(
providers: [
Provider<ClientsProvider>(
create: (context) => ClientsProvider()),
ChangeNotifierProvider<MyProvider>(
create: (context) => MyProvider()),
],
child: Dashboard(),//This widget contains the Child() widget two widgets down.
);
}
}
This is the child widget that needs to be updated when the firebase snapshot updates:
class _ChildState extends State<Child> {
#override
Widget build(BuildContext context) {
return Column(
children: [
_buildAddNew(),
Consumer<ClientsProvider>(
builder: (context, clientProvider, child) {
return Container(child: Text(clientProvider.clients.toString()));
},
),
],
);
}
}
Once again, the error received:
NoSuchMethodError: invalid member on null: 'collection'
The data isn't null, why am I receiving this error?

Answer 1

_fs is null because you never assigned it. Perhaps you meant to do this, as shown in the documentation:
FirebaseFirestore _fs = FirebaseFirestore.instance;