Returning a Future<ExtensionType> generates invalid code

[xvrh]

import 'package:mockito/annotations.dart';

class Foo {
  Future<Id> bar() async => Id(0);
}

extension type Id(int id) {}

@GenerateNiceMocks([MockSpec<Foo>()])
class Test {}

Will generate

class MockFoo extends _i1.Mock implements _i2.Foo {
  @override
  _i3.Future<_i2.Id> bar() =>
      (super.noSuchMethod(
            Invocation.method(#bar, []),
            returnValue: _i3.Future<_i2.Id>.value(0),
            returnValueForMissingStub: _i3.Future<_i2.Id>.value(0),
          )
          as _i3.Future<_i2.Id>);
}

and error: The argument type 'int' can't be assigned to the parameter type 'FutureOr<Id>?'. (argument_type_not_assignable at [mock] test/mock.mocks.dart:34)

[xvrh]

Workaround is to specify a fallbackGenerator:

@GenerateNiceMocks([
  MockSpec<Foo>(fallbackGenerators: {#bar: fallback}),
])
class Test {}

Id fallback() => Id(0);

Still, that could be interesting to generate something working by default?