'Null' can't be assigned to the parameter type 'AccountType Function()'

Is possible that some can explain to me what's going on here. I completely new to flutter and dart programming and I have started a video tutorial on youtube which are using DDD architecture, but I guess the tutorial does not use the new version of flutter which comes with the null safety feature and guess that could the reason why the test is not passing. I just did as in the tutorial and the only differences that I have are the class name and flutter and dart version.

Test output The argument type 'Null' can't be assigned to the parameter type 'AccountType Function()'.

code

import 'package:dartz/dartz.dart';  import 'package:equatable/equatable.dart';  import 'package:flutter_test/flutter_test.dart';  import 'package:matcher/matcher.dart' as matcher;    void main() {    group('AccountType', () {      test('Should return Failure when the value is empty', () {        // arrange        var accountType = AccountType.create('')            .fold((err) => err, (accountType) => accountType);        // assert        expect(accountType, matcher.TypeMatcher<Failure>());      });        test('Should create accountType when value is not empty', () {        // arrange        String str = 'sender';        AccountType accountType = AccountType.create(str).getOrElse(null); <--- Here where the test fails.        // assert        expect(accountType.value, 'sender');      });    });  }    class AccountType extends Equatable {    final String? value;      AccountType._(this.value);      static Either<Failure, AccountType> create(String? value) {      if (value!.isEmpty) {        return Left(Failure('Account type can not be empty'));      } else {        return Right(AccountType._(value));      }    }      @override    List<Object?> get props => [value];  }    class Failure {    final String? message;      Failure(this.message);  }  

https://stackoverflow.com/questions/66910935/null-cant-be-assigned-to-the-parameter-type-accounttype-function April 02, 2021 at 04:08AM