Umbraco Version - UmbracoCms.4.10.1

asp.net version  - 4

Windows and iis version = iis7, windows 7

Stacktrace :

at UCommerce.EntitiesV2.PurchaseOrder.AddProduct(PriceGroup priceGroup, Product product, Int32 quantity, Boolean addToExistingLine)
   at UCommerce.Transactions.TransactionLibraryInternal.AddToBasket(String catalogName, Int32 quantity, String sku, String variantSku, Boolean addToExistingLine, Boolean executeBasketPipeline)
   at Castle.Proxies.Invocations.TransactionLibraryInternal_AddToBasket.InvokeMethodOnTarget()
   at Castle.DynamicProxy.AbstractInvocation.Proceed()
   at UCommerce.Infrastructure.Interceptor.ExceptionLoggingInterceptor.Intercept(IInvocation invocation)
   at Castle.DynamicProxy.AbstractInvocation.Proceed()
   at Castle.Proxies.TransactionLibraryInternalProxy.AddToBasket(String catalogName, Int32 quantity, String sku, String variantSku, Boolean addToExistingLine, Boolean executeBasketPipeline)
   at UCommerce.Api.TransactionLibrary.AddToBasket(Int32 quantity, String sku, String variantSku, Boolean addToExistingLine, Boolean executeBasketPipeline, Nullable`1 catalogId)
   at ASP._Page_macroScripts_Webservice_cshtml.AddToBasket(String addToBasketKey, String quantityKey, Product variant) in ....:line 46
   at ASP._Page_macroScripts_Webservice_cshtml.Execute() in ... 176</span>

Using code from example :

TransactionLibrary.AddToBasket(quantity,
variant.Sku, variant.VariantSku);

And still getting error :

Unit price
cannot be null when adding product to basket.

Even though I found that it should be fixed :

Change log for 3.0.0.12278

FIX: Adding a product without price to basket would cause an exception.

Then the question is, how to add product with variants to the cart without price (it is catalog not shop).

Thank you