NoSuchMethod Error: Method called on null

Question

//in this code i am tring to use connectivity. Android recommended me to add some classes, //getters setter, I added them at the end of the code automatically

    import 'package:firebase_auth/firebase_auth.dart';[enter image description here][1]
    import 'package:flutter/material.dart';
    import 'package:flutter/services.dart';
    import 'signup.dart';
    import 'home.dart';
    import 'dart:async';
    import 'dart:developer' as developer;
    import 'package:flutter/material.dart';
    import 'package:flutter/services.dart';
    
    class Login extends StatefulWidget {
      const Login({Key? key}) : super(key: key);
    
      @override
      _LoginState createState() => _LoginState();
    }
    //loginstate
    class _LoginState extends State<Login> {
      ConnectivityResult? _connectionStatus = ConnectivityResult.none;
      final Connectivity _connectivity = Connectivity();
      late StreamSubscription<ConnectivityResult> _connectivitySubscription;
    
      @override
      void initState() {
        super.initState();
        initConnectivity();
    
        _connectivitySubscription =
            _connectivity.onConnectivityChanged.listen(_updateConnectionStatus);
      }
    
      @override
      void dispose() {
        _connectivitySubscription.cancel();
        super.dispose();
      }
    
      // Platform messages are asynchronous, so we initialize in an async method.
      Future<void> initConnectivity() async {
        late ConnectivityResult result;
        // Platform messages may fail, so we use a try/catch PlatformException.
        try {
          result = await _connectivity.checkConnectivity();
        } on PlatformException catch (e) {
          developer.log('Couldn\'t check connectivity status', error: e);
          return;
        }
    
        // If the widget was removed from the tree while the asynchronous platform
        // message was in flight, we want to discard the reply rather than calling
        // setState to update our non-existent appearance.
        if (!mounted) {
          return Future.value(null);
        }
    
        return _updateConnectionStatus(result);
      }
    
      Future<void> _updateConnectionStatus(ConnectivityResult result) async {
        setState(() {
          _connectionStatus = result;
        });
      }
      //Login function
      static Future<User?> loiginUsingEmailPassword(
          {required String email,
          required String password,
          required BuildContext context}) async {
        FirebaseAuth auth = FirebaseAuth.instance;
        User? user;
        try {
          UserCredential userCredential = await auth.signInWithEmailAndPassword(
              email: email, password: password);
          user = userCredential.user;
        } on FirebaseAuthException catch (e) {
          if (e.code == "user-not-found") {
            print("No user found for that email");
          }
        }
    
        return user;
      }
    
      @override
      Widget build(BuildContext context) {
        //create textfield controller
        TextEditingController _emailController = TextEditingController();
        TextEditingController _passwordController = TextEditingController();
        return Scaffold(
          resizeToAvoidBottomInset: false,
          body: SingleChildScrollView(
            child: Column(
              children: <Widget>[
                Container(
                  padding: EdgeInsets.fromLTRB(15.0, 110.0, 0.0, 0.0),
                  child: Text(
                    'Bon Appétit',
                    style: TextStyle(
                      fontFamily: 'Pacifico',
                      fontSize: 50.0,
                    ),
                  ),
                ),

//new container Container( padding: EdgeInsets.only(top: 35.0, left: 20.0, right: 20.0), child: Column( children: [ TextField( controller: _emailController, decoration: InputDecoration( focusedBorder: UnderlineInputBorder( borderSide: BorderSide(color: Color(0xFFcaa052)), ), labelText: 'EMAIL', labelStyle: TextStyle( fontFamily: 'Alegreya Sans', fontWeight: FontWeight.bold, color: Color(0xFFcaa052), ), ), ), SizedBox( height: 20.0, ), TextField( controller: _passwordController, decoration: InputDecoration( focusedBorder: UnderlineInputBorder( borderSide: BorderSide(color: Color(0xFFcaa052)), ), labelText: 'PASSWORD', labelStyle: TextStyle( fontFamily: 'Alegreya Sans', fontWeight: FontWeight.bold, color: Color(0xFFcaa052), ), ), obscureText: true, ), SizedBox( height: 5.0, ), Container( alignment: Alignment(1.0, 0.0), padding: EdgeInsets.only(top: 15.0, left: 20.0), child: InkWell( child: Text( 'Forgot Password', style: TextStyle( color: Color(0xFF5E0B0B), fontWeight: FontWeight.bold, fontFamily: 'Alegreya Sans', decoration: TextDecoration.underline, ), ), ), ), SizedBox( height: 40.0, ), ], ), ), SizedBox( height: 15.0, ), Container( height: 40.0, width: 400.0, child: Material( borderRadius: BorderRadius.circular(20.0), shadowColor: Color(0xFFffffb1), color: Color(0xFFffd180), elevation: 7.0, child: InkWell( onTap: () async { User? user = await loiginUsingEmailPassword( email: _emailController.text, password: _passwordController.text, context: context); print(user); if (user != null) { Navigator.push( context, MaterialPageRoute(builder: (context) => Home()), ); } }, child: Center( child: Text( 'LOGIN', style: TextStyle( color: Colors.black, fontWeight: FontWeight.bold, fontFamily: 'Alegreya Sans', ), ),

                      ),
                    ),
                  ),
                ),
                Container(
                  child: Text('Connection Status: ${_connectionStatus.toString()}'),
                ),
                SizedBox(
                  height: 15.0,
                ),
                Row(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    Text(
                      'New member?',
                      style: TextStyle(fontFamily: 'Alegreya Sans'),
                    ),
                    SizedBox(
                      width: 5.0,
                    ),
                    InkWell(
                      onTap: () {
                        Navigator.push(
                          context,
                          MaterialPageRoute(builder: (context) => Signup()),
                        );
                      },
                      child: Text(
                        'Sign up',
                        style: TextStyle(
                          color: Color(0xFF5E0B0B),
                          fontWeight: FontWeight.bold,
                          fontFamily: 'Alegreya Sans',
                          decoration: TextDecoration.underline,
                        ),
                      ),
                    ),
                  ],
                ),
              ],
            ),
          ),
        );
      }
    }

//i think because of below code i got error

    class ConnectivityResult {
      static ConnectivityResult? none;
    }
    
    class Connectivity {
      get onConnectivityChanged => null;
    
      checkConnectivity() {}
    }