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I have an MVC controller with a jsonResult that transfers a session cart to Squares CreateOrderRequestLineItem List, but when I Initialize the list the code throws a null exception for quantity because it is a required property. I've mapped the quantity and even straight up set it to a string value I set the property quantity but the null exception is thrown before the code even reaches the mapping. Do I need to set the quantity to not null or 0 if null somewhere? Here is my controller code.

The session cart builds a cart based off of a product class and product model with set values of productid, name, quantity, price, and tax.

How do I map to a new list if it throws a null exception before my code can reach the mapping?

Note: I added another List ItemDetail to transfer the session data after the null exception error was already thrown and this didn't work either.

Note two: when I don't use Square object references and just use my generic lists and return json my quantity shows up with no nulls for every item in my cart.

public JsonResult CheckoutRequest(string id)
 
 List<Item> cart = (List<Item>)Session["cart"];
 List<ItemDetails> itemDetails = cart.Select(s => new ItemDetails
 
 ProductID = Convert.ToInt32(s.Product.ProductID),
 Name = s.Product.Name,
 Price = s.Product.Price,
 Quantity = Convert.ToString(s.Quantity)
 ).ToList();

 var lineItems = itemDetails.Select(s => new CreateOrderRequestLineItem()
 
 Quantity = "1",
 Name = s.Name, 
 BasePriceMoney = new Money
 
 Amount = s.Price,
 Currency = Money.CurrencyEnum.USD,
 ,
 CatalogObjectId = Convert.ToString(s.ProductID),
 ).ToList();

 CreateOrderRequest order = new CreateOrderRequest
 
 ReferenceId = Convert.ToString(Guid.NewGuid()),
 LineItems = lineItems
 ;

 // Configuration.Default.AccessToken = "YOUR_ACCESS_TOKEN";

 var body = new CreateCheckoutRequest
 
 IdempotencyKey = Convert.ToString(Guid.NewGuid()),
 Order = order,
 AskForShippingAddress = true,
 MerchantSupportEmail = "americanapparelusa@aol.com"
 ;

 return Json(new
 
 locationId,
 body
 , JsonRequestBehavior.AllowGet);
 

Please change the following

List<Item> cart = (List<Item>)Session["cart"];

into

List<Item> cart = new List<Item>();
if (Session["cart"] != null && Session["cart"].ToString() != null && Session["cart"].ToString() != "")
 
 cart = JsonConvert.DeserializeObject<List<Item>>(Session["cart"].ToString());

If the Session variable contains List<Item> which potentially has null value, you should use as operator and then check against null value:

var cart = Session["cart"] as List<Item>;
if (cart == null)

 // do something

else

 // use mapping here

However if the Session variable contains JSON data, you can try casting as string type and deserialize it when available:

List<Item> cart = new List<Item>();

if (!string.IsNullOrEmpty(Session["cart"] as string))

 cart = JsonConvert.DeserializeObject<List<Item>>(Session["cart"].ToString());

 // use mapping here

else

 // do something else