somebody ones told me

ProjectCompanyFurniture/ProjectCompanyFurniture/Entities/Invoice.cs

@@ -51,7 +51,7 @@ public class Invoice
             AvailabilityOfPromotionalCode = availabilityOfPromotionalCode,
             DiscountPercentage = discountPercentage,
             SellingPrice = sellingPrice,
-            DateInvoice = DateTime.Now,
+            Date = DateTime.Now,
             Products = products
         };
     }

ProjectCompanyFurniture/ProjectCompanyFurniture/Forms/FormProduct.cs

@@ -50,8 +50,7 @@ namespace ProjectCompanyFurniture.Forms
         {
             try
             {
-                if (string.IsNullOrWhiteSpace(textBoxName.Text)
+                if (string.IsNullOrWhiteSpace(textBoxName.Text) || string.IsNullOrEmpty(textBoxCategory.Text) 
-                    || string.IsNullOrEmpty(textBoxCategory.Text) 
                     || comboBoxManufacturer.SelectedIndex < 0)
                 {
                     throw new Exception("Имеются незаполненные поля");