public ActionResult Completed(int? orderid)
        {
            //validation
            if ((_workContext.CurrentCustomer.IsGuest() && !_orderSettings.AnonymousCheckoutAllowed))
                return new HttpUnauthorizedResult();

            //model
            var model = new CheckoutCompletedModel();
            
           //Added
            if(orderid !=null)
            {

                var o = _orderService.GetOrderById(orderid.Value);
                if(o == null) throw new  Exception("Order cannot be null");
                model.OrderId = o.Id;
                return View(model);
            }
            
            var orders = _orderService.GetOrdersByCustomerId(_workContext.CurrentCustomer.Id);
            if (orders.Count == 0)
                return RedirectToRoute("HomePage");
            else
            {
                
                var lastOrder = orders[0];
                
                model.OrderId = lastOrder.Id;
            }

            return View(model);
        }