An expression tree may not contain a call or invocation that uses optional arguments in moq framework

having trouble with moq after updating project which based on .netcore beta 5 and updated to rc1. Before updating, test was worked and now I have error: "An expression tree may not contain a call or invocation that uses optional arguments". Help me please to solve it.

[Fact]
public async void ReturnPostUserAnswerResult()
{
    // Arrange
    var mockSet = new Mock<DbSet<QuestionsToUsers>>();
    var _applicationDbContext = new Mock<ApplicationDbContext>();
    _applicationDbContext.Setup(a => a.QuestionToUsers).Returns(mockSet.Object);
    var controller = new UserQuizController(_applicationDbContext.Object);
    // Act
    var result = new QuestionsToUsers()
    {
        Answer = true,
        QuestionID = 99,
        TestpackID = 99,
        Id = 99,
        UserID = "TestUser"
    };
    await controller.PostUserAnswerResult(result);

    mockSet.Verify(m => m.Add(It.IsAny<QuestionsToUsers>())); //here error
}