Я получаю ошибку _TypeError при использовании StreamBuilder во флаттере

Question

Попытка изучить шаблон Flutter и Bloc путем создания проверки формы с использованием шаблона Flutter. Кажется, я не понимаю, что не так с моим кодом.

Это файл block.dart

class Bloc extends Object with Validator{
  final _email=StreamController<String>();
  
  Stream<String> get email=>_email.stream.transform(ValidatEmail);

  Function(String) get changeEmail => _email.sink.add;

  dispose(){
    _email.close();
  }
}

final bloc = Bloc();

Вот LoginScreen.dart

class LoginScreen extends StatelessWidget{
  @override
  Widget build(BuildContext context) {
    return Container(
      margin: EdgeInsets.all(20.0),
      child: Column(
        children: [
          emailField(),

        ],
      ),
    );
  }
  Widget emailField(){
    return StreamBuilder(
      stream: bloc.email,
      builder: (context,snapshot){
        return TextField(
          onChanged: bloc.changeEmail,
          keyboardType: TextInputType.emailAddress,
          decoration: InputDecoration(
            errorText: snapshot.error,
            hintText: '[e-mail]',
            labelText: 'Email Address',
          ),
        );
      },
    );
  }
}

Вот Validator.dart

class Validator{
  final ValidatEmail = StreamTransformer<String,String>.fromHandlers(
    handleData: (email,sink){
      if(email.contains('@')){
        sink.add(email);
      }else{
        sink.addError('Enter a valid email');
      }
    }
  );
}

Я получаю следующую ошибку

════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following _TypeError was thrown building LoginScreen(dirty):
type '_AsyncStreamController<dynamic>' is not a subtype of type 'StreamController<String>' of 'function result'

The relevant error-causing widget was: 
  LoginScreen file:///C:/Users/HP/Desktop/Olds/SIH/login_bloc/lib/src/app.dart:9:15
When the exception was thrown, this was the stack: 
#0      Bloc._email (package:loginbloc/bloc/bloc.dart)
#1      Bloc.email (package:loginbloc/bloc/bloc.dart:8:29)
#2      LoginScreen.emailField (package:loginbloc/screen/LoginScreen.dart:22:20)
#3      LoginScreen.build (package:loginbloc/screen/LoginScreen.dart:12:11)
#4      StatelessElement.build (package:flutter/src/widgets/framework.dart:4585:28)