After registration, restarting debugging (Rebuilding the application) of the application, it produces this error ”_TypeError (type ‘Null’ is not a subtype of type ‘bool’)’. Tell me how to fix the error!?

I think that there is an error in this code, because after creating the authorization screen, it gives an error. If you haven’t found the error, I will post it other code!!!!

sign_in_screen.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

import '../../../components/my_text_field.dart';
import '../blocs/sign_in_bloc/sign_in_bloc.dart';

class SignInScreen extends StatefulWidget {
  const SignInScreen({super.key});

  @override
  State<SignInScreen> createState() => _SignInScreenState();
}

class _SignInScreenState extends State<SignInScreen> {
  final passwordController = TextEditingController();
  final emailController = TextEditingController();
  final _formkey = GlobalKey<FormState>();
  bool signInRequired = false;
  IconData iconPassword = CupertinoIcons.eye_fill;
  bool obscurePassword = true;
  String? errorMsg;

  @override
  Widget build(BuildContext context) {
    return BlocListener<SignInBloc, SignInState>(
      listener: (context, state) {
        if (state is SignInSucces) {
          setState(() {
            signInRequired = false;
          });
        } else if (state is SignInProcess) {
          signInRequired = true;
        } else if (state is SignInFailure) {
          signInRequired = false;
          errorMsg = 'Invalid email or password';
        }
      },
      child: Form(
          key: _formkey,
          child: Column(
            children: [
              const SizedBox(
                height: 20.0,
              ),
              SizedBox(
                width: MediaQuery.of(context).size.width * 0.9,
                child: MyTextField(
                  controller: emailController,
                  hintText: 'Email',
                  obscureText: false,
                  keyboardType: TextInputType.emailAddress,
                  prefixIcon: const Icon(CupertinoIcons.mail_solid),
                  errorMsg: errorMsg,
                  validator: (val) {
                    if (val == null ||val.isEmpty) {
                      return 'Please fill in this field';
                    } else if (!RegExp(r'^[w-.]+@([w-]+.)+[w-]{2,4}$')
                        .hasMatch(val)) {
                      return 'Please enter the valid email';
                    }
                    return null;
                  },
                ),
              ),
              const SizedBox(
                height: 10.0,
              ),
              SizedBox(
                  width: MediaQuery.of(context).size.width * 0.9,
                  child: MyTextField(
                    controller: passwordController,
                    hintText: 'Password',
                    obscureText: obscurePassword,
                    keyboardType: TextInputType.visiblePassword,
                    prefixIcon: const Icon(CupertinoIcons.lock_fill),
                    errorMsg: errorMsg,
                    validator: (val) {
                      if (val!.isEmpty) {
                        return ' Please fill the field!';
                      } else if (!RegExp(r'^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9])(?=.*?[!@#$&*~`)%-(_+=;:,.<>/?"[{]}|^]).{8,}$').hasMatch(val)) {
                        return 'Please enter a valid password ';
                      }
                      return null;
                    },
                    suffixIcon: IconButton(
                        onPressed: () {
                          setState(() {
                            obscurePassword = !obscurePassword;
                            if (obscurePassword) {
                              iconPassword = CupertinoIcons.eye_fill;
                            } else {
                              iconPassword = CupertinoIcons.eye_slash_fill;
                            }
                          });
                        },
                        icon: Icon(iconPassword)),
                  )),
              const SizedBox(
                height: 20.0,
              ),
              !signInRequired
                  ? SizedBox(
                      width: MediaQuery.of(context).size.width * 0.5,
                      child: TextButton(
                        onPressed: () {
                          if (_formkey.currentState!.validate()) {
                            context.read<SignInBloc>().add(SignInRequired(
                                emailController.text, passwordController.text));
                          }
                        },
                        style: TextButton.styleFrom(
                            elevation: 3.0,
                            backgroundColor:
                                Theme.of(context).colorScheme.primary,
                            foregroundColor: Colors.white,
                            shape: RoundedRectangleBorder(
                                borderRadius: BorderRadius.circular(60))),
                        child: const Padding(
                          padding: EdgeInsets.symmetric(
                              horizontal: 25, vertical: 5.0),
                          child: Text(
                            'Sign In',
                            textAlign: TextAlign.center,
                            style: TextStyle(
                                color: Colors.white,
                                fontSize: 16.0,
                                fontWeight: FontWeight.w600),
                          ),
                        ),
                      ),
                    )
                  : const CircularProgressIndicator(),
            ],
          )),
    );
  }
}

sign_in_bloc.dart:

import 'package:bloc/bloc.dart';
import 'package:equatable/equatable.dart';
import 'package:user_repository/user_repository.dart';

part 'sign_in_event.dart';
part 'sign_in_state.dart';

class SignInBloc extends Bloc<SignInEvent, SignInState> {
  final UserRepository _userRepository;

  SignInBloc(
    this._userRepository
  ) : super(SignInInitial()) {
    on<SignInRequired>((event, emit) async {
      emit(SignInProcess());
      try {
        await _userRepository.signIn(event.email, event.password);
      } catch (e) {
        emit(SignInFailure());
      }
    });
    on<SignUpRequired>((event, emit) async => await _userRepository.logout());
  }
}

`validator: (val) {
  if (val == null || val.isEmpty) {
    return 'Please fill in this field';
  } else if (!RegExp(r'^[w-.]+@([w-]+.)+[w-]{2,4}$').hasMatch(val)) {
    return 'Please enter the valid email';
  }
  return null;
},`

Here we added a check for val == null in validators.