The getter 'email' was called on null. Receiver: null Tried calling: email Flutter

Question

I added TouchID to my SignIn Page, When i run the code, The app is opening in simulator and I can see the finger print area that i created and when i touch it and try to log in via TouchID i can enter the finger print when it can sense but after that in console, it says

======== Exception caught by widgets library ======================================================= The following NoSuchMethodError was thrown building ProfileScreen(dirty, dependencies: [MediaQuery], state: _ProfileScreenState#7079c): The getter 'email' was called on null. Receiver: null Tried calling: email

The relevant error-causing widget was: ProfileScreen file:///Users/iremguner/AndroidStudioProjects/healtish_app/lib/authenticate/sign_in.dart:77:95 When the exception was thrown, this was the stack: #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5) #1 AuthService.getCurrentUser (package:healtish_app/services/auth.dart:24:30) #2 _ProfileScreenState.build.getProfile (package:healtish_app/ui/pages/profile_screen.dart:73:43) #3 _ProfileScreenState.build (package:healtish_app/ui/pages/profile_screen.dart:243:37) #4 StatefulElement.build (package:flutter/src/widgets/framework.dart:4612:27) ...

and then app is crashing.

import 'package:healtish_app/services/auth.dart';
import 'package:healtish_app/shared/constants.dart';
import 'package:healtish_app/shared/loading.dart';
import 'package:flutter/material.dart';
import 'package:healtish_app/ui/pages/calorie_calculator_screen.dart';
import 'package:healtish_app/ui/pages/profile_screen.dart';
import 'package:flutter/services.dart';
import 'package:local_auth/local_auth.dart';

class SignIn extends StatefulWidget {
  final Function toggleView;

  SignIn({this.toggleView});

   @override
  _SignInState createState() => _SignInState();
 }

  class _SignInState extends State<SignIn> {
   final LocalAuthentication localAuth = LocalAuthentication();
   final AuthService _auth = AuthService();
   final _formKey = GlobalKey<FormState>();
   String error = '';
   bool loading = false;

   // text field state
    String email = '';
    String password = '';

  @override
  Widget build(BuildContext context) {
    return loading
        ? Loading()
        : Scaffold(
        backgroundColor: Color(0xFFE9E9E9),
        appBar: AppBar(
          backgroundColor: Color(0xFFE0AD61),
          elevation: 0.0,
          title: Text(
            'Sign in',
            style: TextStyle(color: Color(0XFF200087), fontSize: 20),
          ),
          actions: <Widget>[
            FlatButton.icon(
              icon: Icon(
                Icons.person,
                color: Color(0XFF200087),
              ),
              label: Text('Register',
                  style: TextStyle(color: Color(0XFF200087), fontSize: 20)),
              onPressed: () => widget.toggleView(),
            ),
          ],
        ),
        body: Container(
          padding: EdgeInsets.symmetric(vertical: 20.0, horizontal: 50.0),
          child: Form(
            key: _formKey,
            child: SingleChildScrollView(
              child: Column(
                children: <Widget>[
                  Hero(
                    tag: 'logo',
                    child: Container(
                        child: Image.asset(
                      'assets/logo.png',
                    )),
                  ),
                  GestureDetector(
                    onTap: () async{
                      bool weCanCheckBiometrics = await localAuth.canCheckBiometrics;
                      if(weCanCheckBiometrics){
                        bool authenticated = await localAuth.authenticateWithBiometrics(
                          localizedReason: "Authenticate to see your bank statement.",
                        );
                        if(authenticated){
                          Navigator.push(context, MaterialPageRoute(builder: (context) => 
                         ProfileScreen()));
                        }
                      }
                    },
                    child: Row(
                      children: <Widget>[
                        Icon(
                          Icons.fingerprint,
                          size: 35.0,
                        ),
                        SizedBox(
                          width: 10,
                        ),
                        Text(
                          "Use Touch Id",
                          style: TextStyle(
                              color: Color(0XFF200087),
                              fontSize: 14,
                              fontWeight: FontWeight.bold),
                        ),
                      ],
                    ),
                  ),
                  Divider(color: const Color(0xFFE3B3D2)),
                  SizedBox(height: 20.0),
                  TextFormField(
                    decoration: textInputDecoration.copyWith(
                        hintText: 'Please Enter Email'),
                    validator: (val) =>
                        val.isEmpty ? 'Enter an email' : null,
                    onChanged: (val) {
                      setState(() => email = val);
                    },
                  ),
                  SizedBox(height: 20.0),
                  TextFormField(
                    obscureText: true,
                    decoration: textInputDecoration.copyWith(
                        hintText: 'Please Enter Password'),
                    validator: (val) => val.length < 6
                        ? 'Enter a password 6+ chars long'
                        : null,
                    onChanged: (val) {
                      setState(() => password = val);
                    },
                  ),
                  SizedBox(height: 20.0),
                  RaisedButton(
                      color: const Color(0XFF200087),
                      child: Text(
                        '  Sign In  ',
                        style: TextStyle(color: Colors.white),
                      ),
                      onPressed: () async {
                        if (_formKey.currentState.validate()) {
                          setState(() => loading = true);
                          dynamic result = await _auth
                              .signInWithEmailAndPassword(email, password);
                          if (result == null) {
                            setState(() {
                              loading = false;
                              error =
                                  'Could not sign in with those credentials';
                            });
                          } else {
                            Navigator.push(
                              context,
                              MaterialPageRoute(
                                  builder: (context) => ProfileScreen(
                                        calorie: 1500.0,
                                      )),
                            );
                          }
                        }
                      }),
                  SizedBox(height: 12.0),
                  Text(
                    error,
                    style: TextStyle(color: Colors.red, fontSize: 14.0),
                  ),
                ],
              ),
            ),
          ),
        ),
      );
  }
}