How can i use this checkbox value within my controller? (System.NullReferenceException: 'Object reference not set to an instance of an object.')

I have a boolean variable within my model assigned as false, which i am then using in my view within a checkbox in order to obtain true or false based on whether the checkbox is ticked or not.

In my view:

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

In my ActionResult:

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


                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 = model.ItemList.itemCheck + Environment.NewLine;

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


            return View();
        }

I have tried to pass this value through 'model.ItemList.itemCheck', however when this ActionResult is executed, i receive a " System.NullReferenceException: 'Object reference not set to an instance of an object.' " error.