showing a error in registerpage in fierbase

gistfile1.txt

import 'package:firebase_auth/firebase_auth.dart';
import 'package:flash_chat/components/paddingButton.dart';
import 'package:flash_chat/constants.dart';
import 'package:flash_chat/screens/chat_screen.dart';
import 'package:flutter/material.dart';

class RegistrationScreen extends StatefulWidget {
  static const String id = '/registration';
  @override
  _RegistrationScreenState createState() => _RegistrationScreenState();
}

class _RegistrationScreenState extends State<RegistrationScreen> {
  final _auth = FirebaseAuth.instance;
  String email;
  String password;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.white,
      body: SingleChildScrollView(
        child: Padding(
          padding: EdgeInsets.symmetric(horizontal: 24.0),
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            crossAxisAlignment: CrossAxisAlignment.stretch,
            children: <Widget>[
              Hero(
                tag: 'logo',
                child: Container(
                  height: 200.0,
                  child: Image.asset('images/logo.png'),
                ),
              ),
              SizedBox(
                height: 48.0,
              ),
              TextField(
                keyboardType: TextInputType.emailAddress,
                textAlign: TextAlign.center,
                onChanged: (value) {
                  email = value;
                },
                decoration: kTextFieldDecration.copyWith(
                  hintText: ' Enter your Email',
                ),
              ),
              SizedBox(
                height: 8.0,
              ),
              TextField(
                obscureText: true,
                textAlign: TextAlign.center,
                onChanged: (value) {
                  password = value;
                },
                decoration: kTextFieldDecration.copyWith(
                  hintText: ' Enter your PassWord',
                ),
              ),
              SizedBox(
                height: 24.0,
              ),
              PaddingButton(
                name: 'Register',
                colors: Colors.blueAccent,
                press: () async {
//                print(email);
//                print(password);
                  try {
                    final newUser = await _auth.createUserWithEmailAndPassword(
                        email: email.trim(), password: password.trim());
                    if (newUser != null) {
                      Navigator.pushNamed(context, ChatScreen.id);
                    }
                  } catch (e) {
                    print(e);
                  }
                },
              ),
            ],
          ),
        ),
      ),
    );
  }
}