Flutter – unexpected null value found

I have tried to run my flutter app and it shows unexpected null value after running,on the debug console it shows that the problem is on the AppText.enText[‘welcome Text:’]!, attached is the code for the auth_page class and apptext class

import 'package:flutter/material.dart';
import 'package:laravel/components/login.dart';
import 'package:laravel/utils/config.dart';
import 'package:laravel/utils/text.dart';

class authPage extends StatefulWidget {
  const authPage({Key? key}) : super(key: key);
  @override
  State<authPage> createState() => _authPage();
}

class _authPage extends State<authPage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Padding(
          padding: const EdgeInsets.symmetric(horizontal: 15, vertical: 15),
          child: SafeArea(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.start,
              crossAxisAlignment: CrossAxisAlignment.start,
              children: <Widget>[
                Text(
                  AppText.enText['welcome Text:']!,
                  style: const TextStyle(
                    fontWeight: FontWeight.bold,
                    fontSize: 36,
                  ),
                ),
                Config.spaceSmall,

                Text(
                  AppText.enText['signIn Text:']!,
                  style: const TextStyle(
                    fontWeight: FontWeight.bold,
                    fontSize: 16,
                  ),
                ),
                Config.spaceSmall,

                //login components here
                loginForm(),
                Config.spaceSmall,
                Center(
                  child: TextButton(
                    onPressed: () {},
                    child: Text(
                      AppText.enText['Forgot Password']!,
                      style: const TextStyle(
                        fontSize: 16,
                        fontWeight: FontWeight.bold,
                        color: Colors.black,
                      ),
                    ),
                  ),
                )

                //18
              ],
            ),
          )),
    );
  }
}

```//
the apptext class//

//class App text
class AppText {
static final enText = {
‘welcome Text’: ‘Welcome’,
‘signIn Text’: ‘signIn to your Account’,
‘Register Text’: ‘Already have an Acount’,
‘Registered Text’:
‘You can easily Sign Up and connect to a doctor near you’,
‘SignUp text’: ‘Dont have an account?’,
‘Social login’: ‘or continue with social account’,
‘Forgot Password’: ‘Forgot your Password’,
};
}

I tried running the app but a red screen appeared showing unexpected null value