我尝试运行我的flutter应用程序，运行后显示意外的空值，在调试控制台上显示问题出在AppText上。enText 'welcome Text：']！，附件是auth_page类和apptext类的代码

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 AppText class AppText { static final enText = { 'welcome Text'：“欢迎”、“登录文本”：'登录到您的帐户'，'注册文本'：“已经有一个Acount”，“注册文本”：“您可以轻松注册并连接到您附近的医生”，“注册文本”：没有账号？'，'社交登录'：'或继续使用社交帐户'，'忘记密码'：'忘记密码'，};}

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