asp mocking error object reference not set to an instance of a object

I get a error when i run my test in asp.net. all my other tests works fine. This is my code in the controller:

public IActionResult CreateTreatment(TreatmentViewModel treatmentViewModel)
        {
            treatmentViewModel.animal = _animalRepository.GetById(treatmentViewModel.animal.ID);
            
            if (treatmentViewModel.animal.PassingAwayDate != null)
            {
                ModelState.AddModelError(string.Empty, "This animal has passed away");
            }

            Animal newAnimal = _animalRepository.GetById(treatmentViewModel.animal.ID);

            

            if (treatmentViewModel.animal.Age == 0)
            {
                //Animal newAnimal = _animalRepository.GetById(treatmentViewModel.animal.ID);
                DateTime date1 = (DateTime)newAnimal.BirthDate;
                var date2 = DateTime.Now;

                var monthscalculated = (date1.Year - date2.Year) * 12 + date2.Month - date1.Month;
                TimeSpan dayscalculated = date2 - date1;

                var totaldays = dayscalculated.TotalDays;

                if (monthscalculated < 6
                    && ((int)treatmentViewModel.Treatment.TreatmentType == 0
                    || (int)treatmentViewModel.Treatment.TreatmentType == 1)
                    && treatmentViewModel.Treatment.AgeRequirement < 6 && totaldays < 180)
                {
                    ModelState.AddModelError(string.Empty, "You cannot do this treatment");
                }

            }

            

            if (ModelState.IsValid)
            {
                Treatment newTreatment = treatmentViewModel.Treatment;


                if ((int)treatmentViewModel.Treatment.TreatmentType == 0 || (int)treatmentViewModel.Treatment.TreatmentType == 1)
                {
                    {
                        var animal = _animalRepository.GetById(treatmentViewModel.animal.ID);
                        animal.NeuteredOrSterilized = true;
                        _animalRepository.UpdateById(animal);
                    }
                }
                if ((int)treatmentViewModel.Treatment.TreatmentType == 3)
                {
                    Comment newComment = new Comment();
                    newComment.CommentString = "Operation";

                    CommentViewModel addCommentViewModel = new CommentViewModel();
                    addCommentViewModel.Comment = newComment;

                    addCommentViewModel.AnimalId = treatmentViewModel.animal.ID;
                   
                    _commentRepository.AddComment(addCommentViewModel.Comment, addCommentViewModel.AnimalId, User.Identity.Name);
                }
                if ((int)treatmentViewModel.Treatment.TreatmentType == 5)
                {
                    Comment newComment = new Comment();
                    newComment.CommentString = "Euthanasia";

                    CommentViewModel addCommentViewModel = new CommentViewModel();
                    addCommentViewModel.Comment = newComment;

                    addCommentViewModel.AnimalId = treatmentViewModel.animal.ID;
                    _commentRepository.AddComment(addCommentViewModel.Comment, addCommentViewModel.AnimalId, User.Identity.Name);
                }
                if ((int)treatmentViewModel.Treatment.TreatmentType == 4)
                {
                    Comment newComment = new Comment();
                    newComment.CommentString = "Chipping GUID: " + Guid.NewGuid();

                    CommentViewModel addCommentViewModel = new CommentViewModel();
                    addCommentViewModel.Comment = newComment;

                    addCommentViewModel.AnimalId = treatmentViewModel.animal.ID;
                    _commentRepository.AddComment(addCommentViewModel.Comment, addCommentViewModel.AnimalId, User.Identity.Name);
                }
                

                    _treatmentRepository.AddTreatment(newTreatment, treatmentViewModel.animal.ID);

                return View("Thanks");
            }
            else
            {
                return View(treatmentViewModel);
            }
        }

This is the code I have in my mocking test. Here I am looking if it makes a comment if i create a operation treatment.

public void BR_4_Explanation_in_treatment_operation()
{
    // Arrange
    var loggerMock = new Mock<ILogger<HomeController>>();
    var animalRepoMock = new Mock<IAnimalRepository>();
    var residenceRepoMock = new Mock<IResidenceRepository>();
    var treatmentRepoMock = new Mock<ITreatmentRepository>();
    var clientapplicationRepoMock = new Mock<IClientAnimalApplicationRepository>();
    var commentRepoMock = new Mock<ICommentRepository>();
    var shoppingCartMock = new Mock<IShoppingCartRepository>();
    var clientMock = new Mock<IClientRepository>();



    var controller = new AnimalController(loggerMock.Object, animalRepoMock.Object, treatmentRepoMock.Object,
        residenceRepoMock.Object,
        commentRepoMock.Object, clientapplicationRepoMock.Object, clientMock.Object, shoppingCartMock.Object);


    
    

    Residence residence = new Residence()
    {
        ID = 1,
        Capacity = 5,
        CatOrDogResidence = "Dog",
        Neutered = true,
        InvidualOrGroup = "group",
        Sex = "Male"

    };

    Volunteer vol = new Volunteer()
    {
        ID = 1,
        Email = "ddjkdkd@hotmail.com",
        Name = "barend",
        DateOfBirth = DateTime.Now,
        PhoneNumber = "dddd"
    };


    Animal an = new Animal()
    {
        ID = 1,
        Adoptable = true,
        Description = "hi",
        Name = "doggo",
        DogOrCat = "Dog",
        ReasonAway = "hi",
        NeuteredOrSterilized = true,
        Photo = "gg",
        Sex = "Male",
        WithChildrenOrNot = "no",
        IncomingDate = DateTime.Now,
        EstimatedAge = 20,
        Residence = residence,
        Age = 20
       
        

    };

    Treatment treatment = new Treatment()
    {
        Animal = an,
        AgeRequirement = 5,
        Costs = 30,
        DateOfTreatment = DateTime.Now,
        Description = "test",
        ID = 1,
        TreatedBy = "barend",
        TreatmentType = TreatmentType.Operation
    };

    


    TreatmentViewModel treatview = new TreatmentViewModel()
    {
        animal = an,
        Treatment = treatment
    };

    Comment comment = new Comment()
    {
        CommentString = "Operation",
        Animal = an,
        CommentMadeBy = vol,
        ID = 1,
        Date = DateTime.Now

    };


    //animalRepoMock.Setup(animal => animal.AddAnimal(an)).Returns(an);

    // treatmentRepoMock.Setup(tr => tr.AddTreatment(treatment, an.ID));
    commentRepoMock.Setup(com => com.AddComment(comment, an.ID, "barend"));
    //act
    
    controller.CreateTreatment(treatview);


    //assert
    commentRepoMock.Verify(ps => ps.AddComment(comment, an.ID, vol.Name), Times.Once);
    
}

When I run this code I get the error on this line: if (treatmentViewModel.animal.PassingAwayDate != null), it says this is null.