System.ArgumentNullException: Value cannot be null. (Parameter 'items')

Question

I'm trying to return a list of LeaveTypes from a model using DropDownListFor. I have found a few topics on this issue, so it seems to be common, and I presume the list needs to be repopulated, but I can't find a way that works (or a way that I understand against the other examples).

I always get the null error regardless of what I do. I'm thinking that maybe actually it is not returning any leavetypes items in the first place, but I'm not understanding the way dropdownlist works with a model.

Is there a different issue causing the null that I can't see right now? view :

`   <div class="form-group">
<label asp-for="LeaveTypeId" class="control-label"></label>@Html.DropDownListFor(q => q.LeaveTypeId, new SelectList(Model.LeaveTypes,
"Value", "Text"), "Select Leave Type", new { @class = "form-control" })<span asp-validation-for="LeaveTypeId" class="text-danger"></span>
            </div>`

I define the list in a class:

  public class CreateLeaveRequestVM
    {
        [Display(Name = "Start Date")]
        [Required]
        public string StartDate { get; set; }
        [Display(Name = "End Date")]
        [Required]
        public string EndDate { get; set; }
        public IEnumerable<SelectListItem> LeaveTypes  { get; set; } // the value here is null why ? 
        [Display(Name ="Leave Type")]
        public int LeaveTypeId { get; set; }
        [Display(Name = "Employee Comments")]
        [MaxLength(300)]
        public string RequestComments { get; set; }

    }

Controller is :

 // GET: LeaveRequestController/Create
        public ActionResult Create()
        {
            var leaveTypes = _leaveTypeRepo.FindAll();
            var leaveTypeItems = leaveTypes.Select(q => new SelectListItem { 
                Text = q.Name,
                Value = q.Id.ToString()
            });
            var model = new CreateLeaveRequestVM
            {
                LeaveTypes = leaveTypeItems
            };
            return View(model);
        }

        // POST: LeaveRequestController/Create
        [HttpPost]
        [ValidateAntiForgeryToken]
        public ActionResult Create(CreateLeaveRequestVM model)
        {
            try
            {
                var startDate = Convert.ToDateTime(model.StartDate);
                var endDate = Convert.ToDateTime(model.EndDate);
                var leaveTypes = _leaveTypeRepo.FindAll();
                var leaveTypeItems = leaveTypes.Select(q => new SelectListItem
                {
                    Text = q.Name,
                    Value = q.Id.ToString()
                });
                model.LeaveTypes = leaveTypeItems;
                if (!ModelState.IsValid)
                {
                    return View(model);
                }

                if (DateTime.Compare(startDate, endDate) > 1)
                {
                    ModelState.AddModelError("", "Start date cannot be further in the future than the end date");
                    return View(model);
                }

                var employee = _userManager.GetUserAsync(User).Result;
                var allocation = _leaveAllocRepo.GetLeaveAllocationsByEmployeeAndType(employee.Id, model.LeaveTypeId);
                int daysRequested = (int)(endDate - startDate).TotalDays;

                if (daysRequested > allocation.NumberOfDays) 
                {
                    ModelState.AddModelError("", "You do not have sufficient days for this request!");
                    return View(model);
                }

                var leaveRequestModel = new LeaveRequestVM
                {
                    RequestingEmployeeId = employee.Id,
                    StartDate = startDate,
                    EndDate = endDate,
                    Approved = null,
                    DateRequested = DateTime.Now,
                    DateActioned = DateTime.Now,
                    LeaveTypeId = model.LeaveTypeId,
                    RequestComments = model.RequestComments
                };

                var leaveRequest = _mapper.Map<LeaveRequest>(leaveRequestModel);
                var isSuccess = _leaveRequestRepo.Create(leaveRequest);

                if (!isSuccess)
                {
                    ModelState.AddModelError("", "Something went wrong with submitting your record");
                    return View(model);
                }

                return RedirectToAction("MyLeave");
            }
            catch (Exception)
            {
                ModelState.AddModelError("", "Something went wrong");
                return View(model);
            }
        }

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