when adding a product to basket

TransactionLibrary.AddToBasket(1, product.Sku);
TransactionLibrary.ExecuteBasketPipeline();

I am getting a price cant be null error  because price is not set for product. but I need to be able to have products where prices are not set as they will be comming from an external system.

I tried the folloing check before adding to basket

PriceCalculation price = CatalogLibrary.CalculatePrice(product);

            if (price.YourPrice == null)
            {      

var priceGroup = PriceGroup.SingleOrDefault(x => x.Name == "EUR 15 pct");        
                var productPrice = new PriceGroupPrice
                {
                    Product = product,
                    PriceGroup = priceGroup,
                    Price = 1m
                };

                productPrice.Save(); 

//product = Product.All().Single(x => x.Sku == sku);          
            }

TransactionLibrary.AddToBasket(1, product.Sku);
TransactionLibrary.ExecuteBasketPipeline();

this does indeed set the price however the page still crashes. but the nexttime you try to add the product it works ok.

even tried reloading product after adding price (commented out above) but still no joy.

any sugestions.