Null Reference exception was unhandled by user code and item is null - asp.net-mvc

Question

This working but all of a sudden it stopped working and was throwing null reference exception, when i checked in my basket record was inserted but the item is still null: the error is around BasketItem item = basket.BasketItems.FirstOrDefault(i => i.product_Id == product_Id);
using my_eCommerce.Contracts.Repositories;
using my_eCommerce.Model;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Web;
namespace my_eCommerce.Services
{
public class BasketService
{
IRepositoryBase<Basket> baskets;
public const string BasketSessionName = "eCommerceBasket";
public BasketService(IRepositoryBase<Basket> baskets)
{
this.baskets = baskets;
}
private Basket CreateNewBasket(HttpContextBase httpContext)
{
//create a new basket
//
//ffirst ceate a new cookie
HttpCookie cookie = new HttpCookie(BasketSessionName);
// Now create a new Basket and set the creation date
Basket basket = new Basket();
//basket.BasketId = Guid.NewGuid(); //basket.BasketId = Guid.NewGuid() is supposed to come after date;
basket.Basket_Id = Guid.NewGuid();
basket.date = DateTime.Now;
baskets.Insert(basket);
baskets.Commit();
//Add basketId to a cookie
cookie.Value = basket.Basket_Id.ToString();
cookie.Expires = DateTime.Now.AddDays(1);
httpContext.Response.Cookies.Add(cookie);
return basket;
}
public bool AddToBasket(HttpContextBase httpContext, int product_Id, int quantity)
{
bool succcess = true;
Basket basket = GetBasket(httpContext);
//BasketItem item = basket.BasketItems.FirstOrDefault(i => i.product_Id == product_Id);
BasketItem item = basket.BasketItems.FirstOrDefault(i => i.product_Id == product_Id);
if (item == null)
{
item = new BasketItem()
{
Basket_Id = basket.Basket_Id,
product_Id = product_Id,
Quantity = quantity
};
basket.BasketItems.Add(item);
}
else
{
item.Quantity = item.Quantity + quantity;
}
baskets.Commit();
return succcess;
}
public Basket GetBasket(HttpContextBase httpContext)
{
HttpCookie cookie = httpContext.Request.Cookies.Get(BasketSessionName);
Basket basket;
Guid basket_Id;
if (cookie != null)
{
if (Guid.TryParse(cookie.Value, out basket_Id))
{
basket = baskets.GetById(basket_Id);
}
else
{
basket = CreateNewBasket(httpContext);
}
}
else
{
basket = CreateNewBasket(httpContext);
}
return basket;
}
}
}

Answer 1

Your basket or basket.BasketItems objects could be null in some situations. You should put Null check for this object the way you have done for the item object. Try to rewrite the code in the following way:
...
BasketItem item = null;
Basket basket = GetBasket(httpContext);
if(basket != null && basket.BasketItems != null)
{
item = basket.BasketItems.FirstOrDefault(i => i.product_Id == product_Id);
}
if (item == null)
{
...

Answer 2

Use Null-conditional operators ?.
You can use it like below and it will not throw exception but it will return
null if basket is null.
null if basket.BasketItems is null.
Or FirstOrDefault() value from basket.BasketItems
BasketItem item = basket?.BasketItems?.FirstOrDefault(i => i.product_Id == product_Id);