无法将值 NULL 插入到列（字符串格式列）[关闭]

问：

SqlException：无法将值 NULL 插入到表“Nhom9BH.dbo.HoaDon”的列“Address”中;列不允许 null。INSERT 失败。该声明已被终止。 我只是看了一些 youtube 视频，它是关于 Id 等列的，我的情况是一个字符串，我无法用这些解决方案修复。有人可以帮我吗 我的行动：

public IActionResult Checkout()
 {
     var identity = (ClaimsIdentity)User.Identity;
     var claim = identity.FindFirst(ClaimTypes.NameIdentifier);
     CartViewModel Cart = new CartViewModel()
     {
         CartList = _db.Cart.Include("Product")
         .Where(gh => gh.ApplicationUserId == claim.Value)
         .ToList(),
         Bill = new Bill()
     };
     Cart.Bill.ApplicationUser = _db.ApplicationUser.FirstOrDefault(user => user.Id == claim.Value);
     Cart.Bill.Name = Cart.Bill.ApplicationUser.Name;
     Cart.Bill.Address = Cart.Bill.ApplicationUser.Address;
     Cart.Bill.PhoneNumber = Cart.Bill.ApplicationUser.PhoneNumber;
     foreach (var item in Cart.CartList)
     {
         item.ProductPrice = item.Quantity * item.Product.Price;
         Cart.Bill.TotalPrice += item.ProductPrice;
     }
     return View(Cart);
 }
 [HttpPost]
 [ValidateAntiForgeryToken]
 public IActionResult Checkout(CartViewModel Cart)
 {
     var identity = (ClaimsIdentity)User.Identity;
     var claim = identity.FindFirst(ClaimTypes.NameIdentifier);

     Cart.CartList = _db.Cart.Include(x => x.Product)
         .Where(gh => gh.ApplicationUserId == claim.Value)
         .ToList();
     if (Cart.Bill == null)
     {
         Cart.Bill = new Bill();
     }
     Cart.Bill.ApplicationUserId = claim.Value;
     Cart.Bill.OrderDate = DateTime.Now;
     Cart.Bill.OrderStatus = "Confirming";


     foreach (var item in Cart.CartList)
     {
         item.ProductPrice = item.Quantity + item.Product.Price;
         Cart.Bill.TotalPrice += item.ProductPrice;
     }

     _db.Bill.Add(Cart.Bill);
     _db.SaveChanges();

     foreach (var item in Cart.CartList)
     {
         BillDetail BillDetail = new BillDetail()
         {
             ProductId = item.ProductId,
             BillId = Cart.Bill.Id,
             ProductPrice = item.ProductPrice,
             Quantity = item.Quantity
         };

         _db.BillDetail.Add(BillDetail);
         _db.SaveChanges();
     }
     _db.Cart.RemoveRange(Cart.CartList);
     _db.SaveChanges();
     return RedirectToAction("Index", "Home");

 }

我尝试观看印度视频，但找不到任何合适的解决方案