@Test
public void testGetUserDetailsNullResult() {

    doAnswer(new Answer() {
        @Override
        public Object answer(InvocationOnMock invocation) throws Throwable {
            ((UserDataStore.UserDetailsCallback) invocation.getArguments()[1]).onUserEntityLoaded(
                    mockUserEntity);
            return null;
        }
    }).when(cloudUserDataStore).getUserEntityDetails(anyInt(),
            any(UserDataStore.UserDetailsCallback.class));
    given(mockUserEntityDataMapper.transform(mockUserEntity)).willReturn(null);
    doNothing().when(mockUserDetailsRepositoryCallback).onError(any(RepositoryErrorBundle.class));
    userDataRepository.getUserById(FAKE_USER_ID, mockUserDetailsRepositoryCallback);
    verify(mockUserEntityDataMapper).transform(mockUserEntity);
    verify(mockUserDetailsRepositoryCallback).onError(any(RepositoryErrorBundle.class));
}