My data from firestore not retrieve using dart flutter - firebase

Question

I am using cloud fire store in flutter I did:
connected the app with the firebase
put the google-services.json in app buil.gradle
add the dependency and plugin
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
MyApp();
#override
Widget build(BuildContext context) {
// TODO: implement build
return MaterialApp(
title: 'کوردی پۆلی یەک',
theme: ThemeData(
primarySwatch: Colors.blueGrey,
),
home: MainScreen(),
);
}
}
class MainScreen extends StatelessWidget{
List<Widget> makeListWidget(AsyncSnapshot snapshot){
return snapshot.data.documents.map<Widget>((document){
return ListTile(
title: Text(document["name"]),
);
}).toList();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("کوردی پۆلی یەک",style: TextStyle(color: Colors.white),),
backgroundColor: Colors.deepOrange,
),
body: Container(
child: StreamBuilder(
stream: Firestore.instance.collection('lesson').snapshots(),
builder: (context,snapshot){
switch(snapshot.connectionState){
case ConnectionState.none:
return Center(child: Text('No data'));
case ConnectionState.waiting:
return Center(
child:CircularProgressIndicator());
default:
return ListView(
children:makeListWidget(snapshot),
);
}
},
),
),
);
}
}
It is just loading and when ever I delete the connectionState.waiting gives me error:
NoSuchMethodError: The getter 'documents' was called on null. Receiver: null
Tried calling

Answer 1

Change the firestore security rules to the following:
// Allow read/write access to all users under any conditions
// Warning: **NEVER** use this rule set in production; it allows
// anyone to overwrite your entire database.
service cloud.firestore {
match /databases/{database}/documents {
match /{document=**} {
allow read, write: if true;
}
}
}

Answer 2

change the allow read, write: if true; to allow read, write;