Why does this value in my model return null when used in my controller? (ASP.NET MVC)

Question

within my model i have a bool value called itemCheck:

public class Item
    {       
        public Array userDataItems { get; set; }

        public char[] delimiterChar { get; set; }

        public bool itemCheck { get; set; }

    }

My viewModel, linking the item model to the controller:

public class CategoryItemViewModel
    {
        public Item ItemList { get; set; }

        public Category CategoryList { get; set; }
    }

Which i then initialize within my main controller as false:

public ActionResult Index()
        {
            CategoryItemViewModel CIVM = new CategoryItemViewModel();
            CIVM.ItemList = GetItemModel();
            CIVM.CategoryList = GetCategoryModel();
            return View(CIVM);
        }

 public Item GetItemModel()
        {
            var dataFileItems = Server.MapPath("~/App_Data/Item.txt");

            Item iModel = new Item()
            {
                userDataItems = System.IO.File.ReadAllLines(dataFileItems), //Items Text File
                delimiterChar = new[] { ',' },
                itemCheck = false,
            };

            return iModel;
        }

Then i use it in my view as the bool value to indicate whether a checkbox is ticked or not:

@using (Html.BeginForm("Items", "Items", FormMethod.Post, new { id = "formFieldTwo" }))
        {
            @Html.CheckBoxFor(m => m.ItemList.itemCheck, false)
        }

And lastly i try to access this variable 'itemCheck' which should be set to 'false' within my ActionResult:

[HttpPost]
        public ActionResult Items(string ItemDescription, CategoryItemViewModel m)
        {

            bool originalValue = m.ItemList.itemCheck;

            var FkFile = Server.MapPath("~/App_Data/ForeignKeyValue.txt");

            var Fk = System.IO.File.ReadAllText(FkFile);

            var dataFileItems = Server.MapPath("~/App_Data/Item.txt");

            var numberOfLinesItems = System.IO.File.ReadLines(dataFileItems).Count();

            var textFileDataItems = ItemDescription + "," + numberOfLinesItems + "," + Fk + "," + originalValue + Environment.NewLine;

            System.IO.File.AppendAllText(dataFileItems, textFileDataItems);

            return View();
        }

However, i get the following error on the line 'bool originalValue = m.ItemList.itemCheck;':

" System.NullReferenceException: 'Object reference not set to an instance of an object.' "

I fail to understand why my program is giving me this error?

Answer 1

Change:

 @Html.CheckBoxFor(m => m.ItemList.itemCheck, false)

To:

 @Html.CheckBoxFor(Model => Model.ItemList.itemCheck, false)