Flutter – null check operator is used on a null value appear when the current user logout

If I run the app and the last user account stays logged and click on logs out, this null check operator is used on a null value is what appears in the emulator, and I don’t know where the exact error to solve it.

this is my main.dart code

import 'dart:async';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:google_mobile_ads/google_mobile_ads.dart';
import 'package:provider/provider.dart';
import 'package:water_reminder_app/screens/home_page.dart';
import 'package:water_reminder_app/screens/start_page.dart';
import 'package:water_reminder_app/services/notify_service.dart';
import 'package:water_reminder_app/widgets/database.dart';
import 'package:water_reminder_app/widgets/user_data.dart';
import 'firebase_options.dart';
import 'package:firebase_core/firebase_core.dart';
import 'model/pages_names.dart';

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  unawaited(MobileAds.instance.initialize());

  await NotificationServices().init();
  await Firebase.initializeApp(options: DefaultFirebaseOptions.currentPlatform);

  runApp(
    ChangeNotifierProvider(
        create: (context) => CloudDataProvider(), child: const MyApp()),
  );
}

class MyApp extends StatefulWidget {
  const MyApp({
    super.key,
  });

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  String? profileImagePath;
  User? user;

  @override
  void initState() {
    super.initState();
    user = FirebaseAuth.instance.currentUser;
  }

  @override
  Widget build(BuildContext context) {
    final cloudDataProvider =
        Provider.of<CloudDataProvider>(context, listen: false);
    final weight = cloudDataProvider.weight;
    final unit = cloudDataProvider.unit;
    final bedtime = cloudDataProvider.bedtime;
    final wakeUpTime = cloudDataProvider.wakeUptime;

    return MultiProvider(
      providers: [
        ChangeNotifierProvider(
          create: (context) => UserDataProvider(),
        ),
        ChangeNotifierProvider(
          create: (context) => CloudDataProvider(),
        ),
      ],
      child: MaterialApp(
        debugShowCheckedModeBanner: false,
        home: user == null
            ? const StartPage()
            : HomePage(
                weight: weight ?? 0,
                unit: unit ?? '',
                bedTime: bedtime ?? '',
                wakeUpTime: wakeUpTime ?? ''),
        onGenerateRoute: MyRoutes.genrateRoute,
      ),
    );
  }
}

And this is the CloudDataProvider file

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/cupertino.dart';

class CloudDataProvider extends ChangeNotifier {
  double? weight;
  String? unit;
  String? bedtime;
  String? wakeUptime;

  void fetchUserData() async {
    final User? user = FirebaseAuth.instance.currentUser;

    if (user != null) {
      final userDoc =
          FirebaseFirestore.instance.collection('users').doc(user.uid);

      final userSnapshot = await userDoc.get();

      weight = userSnapshot['weight'] as double;
      unit = userSnapshot['unit'] as String;
      bedtime = userSnapshot['bedtime'] as String;
      wakeUptime = userSnapshot['wake-up time'] as String;
    }

    notifyListeners();
  }
}

You can find the whole app in this link gitHub link

I tried to use ?? instead of ! that I found it in this link Null check operator used on a null value but the error still there. anyone can know how to fix this problem