type 'Null' is not a subtype of type 'Future<Either<Failure, UnblockingEntity>>

[AhmedEzio47]

Hi, The following error gets thrown and thenAnswer part never gets called: type 'Null' is not a subtype of type 'Future<Either<Failure, UnblockingEntity>>'

That's how I mock my use cases:

class MockUnblockOfferUseCase extends Mock implements UnblockOfferUseCase {}
class MockLogAnalyticsEventUseCase extends Mock
    implements LogAnalyticsEventUseCase {}

That's how I stub their methods:

void arrangeUnblockOfferSuccess() {
    when(() => logAnalyticsEventUseCase.call(
            LogEventParams(event: AnalyticsEvents.unlockOffer, params: null)))
        .thenAnswer((_) async => const Right(null));

    when(() => unblockOfferUseCase.call(defaultOfferParams))
        .thenAnswer((_) async => Right(UnblockingEntity(code: 'test')));
  }

This is my test:

blocTest<ActivationBloc, ActivationState>(
        'check that UnblockOfferUseCase gets called',
        setUp: () {
          arrangeUnblockOfferSuccess();
        },
        build: () => sut,
        act: (bloc) =>
            bloc.add(OfferUnblocked(offerId: defaultOfferParams.offerId)),
        verify: (_) {
          verify(() => unblockOfferUseCase.call(defaultOfferParams)).called(1);
        });

This is the first use case:

class UnblockOfferUseCase extends UseCase<UnblockingEntity, OfferParams> {
  final OfferRepository offerRepository;

  UnblockOfferUseCase({required this.offerRepository});
  @override
  Future<Either<Failure, UnblockingEntity>> call(OfferParams params) async {
    return await offerRepository.unblock(offerId: params.offerId);
  }
}

class OfferParams {
  final String offerId;

  OfferParams({required this.offerId});
}

This is the second use case

class LogAnalyticsEventUseCase extends UseCase<void, LogEventParams> {
  final FirebaseAnalyticsRepository firebaseAnalyticsRepository;
  final CleverTapRepository cleverTapRepository;

  LogAnalyticsEventUseCase({
    required this.firebaseAnalyticsRepository,
    required this.cleverTapRepository,
  });
  @override
  Future<Either<Failure, void>> call(LogEventParams params) async {
    firebaseAnalyticsRepository.logEvent(
        event: params.event, params: params.params);
    cleverTapRepository.logEvent(event: params.event, params: params.params);
    return const Right(null);
  }
}

class LogEventParams {
  final String event;
  final Map<String, dynamic>? params;

  LogEventParams({required this.event, required this.params});
}

I've also tried the solutions from other similar issues but with no luck. @felangel , please have a look at this.