The getter 'uid' was called on null - but only half the time - firebase

Question

So I have this screen in my Flutter app that is supposed to show all the notes for a particular user. I have the Firestore structured so that there is a collection of notes and each user has one document named their uid. Then all their notes are store in a collection (usernotes) under their document.
The problem I am having here is that when you try to access the notes page in the app, you get the error
The getter 'uid' was called on null.
Receiver: null
Tried calling: uid
But when I simply click run from the Flutter app, everything works just fine. You can see all the notes on the screen. Here is my note screen.
import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'welcome_screen.dart';
class NoteScreen extends StatefulWidget {
static const String id = 'note_screen';
#override
_NoteScreenState createState() => _NoteScreenState();
}
class _NoteScreenState extends State<NoteScreen> {
final _auth = FirebaseAuth.instance;
User loggedInUser;
#override
void initState() {
super.initState();
getCurrentUser();
}
void getCurrentUser() async {
try {
final user = await _auth.currentUser;
if (user != null) {
loggedInUser = user;
}
} catch (e) {
print(e);
}
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Field Notes'),
actions: <Widget>[
IconButton(
icon: const Icon(Icons.chat),
tooltip: 'Messages',
onPressed: () {},
),
IconButton(
icon: const Icon(Icons.exit_to_app),
tooltip: 'Log Out',
onPressed: () {
_auth.signOut();
Navigator.pushNamed(context, WelcomeScreen.id);
},
),
],
),
body: StreamBuilder(
stream: FirebaseFirestore.instance
.collection('notes').doc(loggedInUser.uid).collection('usernotes')
.snapshots(),
builder: (ctx, streamSnapShot) {
if(!streamSnapShot.hasData) return const Text('Loading...');
if (streamSnapShot.connectionState == ConnectionState.waiting) {
return Center(
child: CircularProgressIndicator(),
);
}
final noteData = streamSnapShot.data.docs;
return ListView.builder(
itemCount: noteData.length,
itemBuilder: (ctx, index) => Container(
padding: EdgeInsets.all(8),
child: Text(noteData[index]['text']),
),
);
},
),
floatingActionButton:
FloatingActionButton(child: Icon(Icons.add), onPressed: () {
FirebaseFirestore.instance.collection('notes').doc(loggedInUser.uid).collection('usernotes').add({
'text' : 'This was added by clicking the button!'
});
}),
);
}
}

Answer 1

currentUser is of type User therefore you do not need to use await since it doesn't return a Future. You can do the following:
FirebaseFirestore.instance.collection('notes').doc(_auth.currentUser.uid).collection('usernotes').snapshots(),
And:
FloatingActionButton(child: Icon(Icons.add), onPressed: () {
FirebaseFirestore.instance.collection('notes').doc(_auth.currentUser.uid).collection('usernotes').add({'text' : 'This was added by clicking the button!'});
});