Flutter Unhandled Exception: NoSuchMethodError: The getter 'uid' was called on null - flutter

Question

First of all, I would like to say I have seen all the previous posts on this error but none of them resolved my issue and that's why I am posting it.
Actually, I have understood the problem but unable to resolve it. So, the below dart file is my HomeScreen().
import 'package:flutter/material.dart';
import 'package:intl/intl.dart';
import 'package:mukti/authentication/firestore_service.dart';
import 'package:mukti/schedule/task.dart';
import 'package:mukti/schedule/taskdata.dart';
import 'package:provider/provider.dart';
import 'add_class.dart';
import 'package:firebase_auth/firebase_auth.dart' as auth;
class HomeScreen extends StatefulWidget {
static final String routeName = 'homeScreen';
final auth.User firebaseUser;
HomeScreen({this.firebaseUser});
#override
_HomeScreenState createState() => _HomeScreenState();
}
class _HomeScreenState extends State<HomeScreen> {
final FirestoreService firestoreService = FirestoreService();
#override
Widget build(BuildContext context) {
print("HomeScreen");
print(widget.firebaseUser);
return Scaffold(
body: SafeArea(
child: SizedBox.expand(
child: Padding(
padding: const EdgeInsets.all(48.0),
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.start,
children: [
SingleChildScrollView(
child: Container(
width: MediaQuery.of(context).size.width,
height: 450,
color: Colors.yellow[100],
child: generateTaskList(),
),
),
SizedBox(height: 45),
/* Add Class Button */
Center(
child: GestureDetector(
onTap: () {
Navigator.push(
context, MaterialPageRoute(
builder: (context) => AddClass(),
),
);
},
child: Container(
height: 75,
width: 75,
decoration: BoxDecoration(
shape: BoxShape.circle,
boxShadow: [
BoxShadow(
color: Colors.grey,
offset: Offset(0, 4), //(x,y)
blurRadius: 1.0,
),
],
color: Color(0xFFF9A826),
),
child: Icon(
Icons.add,
size: 35,
color: Colors.white,
),
),
),
),
],
),
),
),
),
);
}
Widget generateTaskList() {
//print("Firebase User : ${widget.firebaseUser.uid}");
Provider.of<TaskData>(context, listen: false).loadTaskList(widget.firebaseUser);
print('List Generated');
var taskListLength = Provider.of<TaskData>(context, listen: false).getTaskListCount();
return Consumer<TaskData>(
builder: (context, taskData, child) => ListView.builder(
itemCount: taskData.taskList.length,
itemBuilder: (context, index) {
print("TaskList");
return Container(
padding: EdgeInsets.all(16.0),
decoration: new BoxDecoration (
borderRadius: BorderRadius.circular(10),
color: Color(0xFFF9A826),
),
child: ListTile(
title: Text(
taskData.taskList[index].description ?? 'default',
style: TextStyle(
color: Colors.white,
fontWeight: FontWeight.w600,
),
),
subtitle: Text(
"${Util.getFormattedDate(taskData.taskList[index].scheduledDateTime)}" ?? 'default',
style: TextStyle(
color: Colors.white54,
),
),
),
);
}
)
);
}
}
class Util {
static String getFormattedDate(DateTime dateTime) {
return new DateFormat("EEE, MMM d, y").format(dateTime);
}
}
Initially, firebaseUser is not null, I have crossed checked it and it is printing the data in the app but when I add more entries from AddClass() and returns to HomeScreen() again, firebaseUser becomes null and no data is shown in the app anymore.
The below code is my AddClass() code:
import 'package:flutter/material.dart';
import 'package:mukti/authentication/authService.dart';
import 'package:mukti/authentication/firestore_service.dart';
import 'package:mukti/schedule/scheduled_date.dart';
import 'package:mukti/schedule/task.dart';
import 'package:mukti/ui_pages/main_screen/timepicker.dart';
import 'package:provider/provider.dart';
import 'package:table_calendar/table_calendar.dart';
import 'package:firebase_auth/firebase_auth.dart' as auth;
import 'home_screen.dart';
class AddClass extends StatefulWidget {
static final String routeName = 'addClass';
#override
_AddClassState createState() => _AddClassState();
}
class _AddClassState extends State<AddClass> {
final FirestoreService firestoreService = FirestoreService();
#override
Widget build(BuildContext context) {
print("Add Class Screen");
return Scaffold(
resizeToAvoidBottomInset: false,
backgroundColor: Color(0xFFFFFFE5),
body: SafeArea(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: [
/* Meeting url TextField Widget */
/* Description TextField Widget */
/* Calender */
/* Add Class Button */
Expanded(
child: GestureDetector(
onTap: () async{
auth.User firebaseUser = await Provider.of<AuthService>(context, listen: false).getUser();
DateTime scheduledDateTime = Provider.of<ScheduledDate>(context, listen: false).scheduledDateTime;
print(scheduledDateTime);
print(firebaseUser);
final task = Task(
link: 'xyz',
isDone: false,
description: 'xyz',
scheduledDateTime: scheduledDateTime,
);
firestoreService.addTask(firebaseUser, task);
print('Task Added');
Navigator.popAndPushNamed(context,
HomeScreen.routeName,
arguments: firebaseUser,
);
},
child: Align(
alignment: FractionalOffset.bottomCenter,
child: Container(
height: 50,
width: MediaQuery.of(context).size.width,
decoration: BoxDecoration(
color: Color(0xFFF9A826),
),
child: Center(
child: Text(
'SCHEDULE CLASS',
style: Theme.of(context).textTheme.bodyText1.copyWith(
color: Colors.white,
fontWeight: FontWeight.w700,
fontSize: 16,
letterSpacing: 0.5,
),
)
)
),
),
),
),
],
),
),
);
}
}
Actually, I have removed unnecessary codes, so after adding one more class to the database, I return to HomeScreen but this time firebaseUser becomes null, although I am sending it in the argument of the routes HomeScreen is receiving null. This is my problem.
How can I resolve this..?
If anyone needs more information, feel free to ask me.
Thanks