private Notification(SupplierOffer supplierOffer)
        {
            if (supplierOffer == null)
            {
                throw new ArgumentNullException();
            }

            SupplierOffer = supplierOffer;
            DateTime      = DateTime.Now;
        }
 public static Notification OfferCreated(SupplierOffer supplierOffer)//factoty method
 {
     return(new Notification(supplierOffer));
 }