Html.HiddenFor helper throwing null exception - asp.net-mvc

Question

I want to pass a value from the model...
#Html.HiddenFor(model => model.ProductId)
Exception thrown: 'System.ArgumentException' in System.Web.Mvc.dll
Additional information: Value cannot be null or empty.
But it is throwing this exception and I don't know why... And no ProductId isn't null.
Action
[HttpGet]
public ActionResult Edit(int ProductId = 0)
{
PCsViewModel pcViewModel = new PCsViewModel();
ProductRepository productRepo = new ProductRepository();
Product dbProduct = productRepo.GetAll(item=>item.ID==ProductId);
PCsRepository pcsRepo = new PCsRepository();
PC dbPC = pcsRepo.GetAll(item=>item.ProductID==ProductId);
if (dbProduct != null && dbPC != null)
{
pcViewModel = new PCsViewModel(dbProduct,dbPC);
}
return View(pcViewModel);
}
ViewModel
public int ProductId { get; set; }
[Required]
public string Name { get; set; }
public string PCsInfo { get; set; }//for the front view
[Required]
public double Price { get; set; }
[Required]
public string ImagePath { get; set; }
[Required]
public string Processor { get; set; }
[Required]
public string OS { get; set; }
[Required]
public int RAM { get; set; }
[Required]
public int Storage { get; set; }
[Required]
public string VideoCard { get; set; }
[Required]
public int CategoryID { get; set; }
public PCsViewModel()
{
}
public PCsViewModel(Product product, PC pc)
{
this.ProductId = product.ID;
this.CategoryID = product.CategoryID;
this.OS = product.OS;
this.Processor = product.Processor;
this.Name = product.Name;
this.RAM = product.RAM;
this.Storage = product.Storage;
this.VideoCard = pc.VideoCard;
this.PCsInfo = "PC "+product.Name + "with processor " + product.Processor;
this.Price = (double)product.Price;
this.ImagePath = Path.Combine(Constants.ImagesPCsDirectory, product.ImageName);
}

Answer 1

Based of the discussion in the comments, it looks like your actual issue wasn't related to the ProductId property but instead your ImagePath property, which was being passed into a Url.Content() helper (to resolve the appropriate path).
This would work as expected if the path existed, but if that property was null or empty, you would receive the ArgumentNullException that you currently are. The best approach would likely be to just only render the specific path if that specific property wasn't null:
#if (!string.IsNullOrEmpty(Model.ImagePath)) {
// Use Url.Content(Model.ImagePath) within here safely
}
There are multiple different ways to handle this, such as adding an additional property on your model to clean things up:
public bool HasImage => !string.IsNullOrEmpty(ImagePath);
And then use:
#if (Model.HasImage) {
// Use Url.Content(Model.ImagePath) within here safely
}