Deleting one object from CartItems in razor pages - asp.net-core

Question

i have some products in my Cart via cookies, now i want to select and delete them from cart,
public class CartModel : PageModel
{
public List<CartItem> CartItems;
public const string CookieName = "cart-items";
public void OnGet()
{
var serializer = new JavaScriptSerializer();
var value = Request.Cookies[CookieName];
CartItems = serializer.Deserialize<List<CartItem>>(value); //error accurred in this line
foreach (var item in CartItems)
item.TotalItemPrice = item.UnitPrice * item.Count;
}
public IActionResult OnGetRemoveFromCart(long id)
{
var serializer = new JavaScriptSerializer();
var value = Request.Cookies[CookieName];
Response.Cookies.Delete(CookieName);
var cartItems = serializer.Deserialize<List<CartItem>>(value);
var itemToRemove = cartItems.FirstOrDefault(x => x.Id == id);
cartItems.Remove(itemToRemove);
var options = new CookieOptions { Expires = DateTime.Now.AddDays(2) };
Response.Cookies.Append(CookieName, serializer.Serialize(cartItems), options);
return RedirectToPage("/Cart");
}
until i don't click on the delete button, everything is ok, i don't have any error in OnGet on Cart Razor page. but when i click on the delete button and OnGetRemoveFromCart's handler is executed,CartItems is null on OnGet!
the errorr: 'Object reference not set to an instance of an object.CartItems was null.'

Answer 1

Response.Cookies.Delete(CookieName);
You delete the cookie in the OnGetRemoveFromCart handler, so value becomes null in the OnGet handler. You should always check for null before accessing cookie values:
public void OnGet()
{
var serializer = new JavaScriptSerializer();
var value = Request.Cookies[CookieName];
if(value is not null)
{
CartItems = serializer.Deserialize<List<CartItem>>(value);
foreach (var item in CartItems)
{
item.TotalItemPrice = item.UnitPrice * item.Count;
}
}
}