An error occurred while attaching module (Dynamicweb.Frontend.Content)

System.NullReferenceException: Object reference not set to an instance of an object.
   at Dynamicweb.Ecommerce.Indexing.ProductQueryHelper.LoadFacets(IQuery query, IEnumerable`1 facetGroups)
   at Dynamicweb.Ecommerce.Indexing.ProductQueryHelper.CreateQuerySettings(ProductCatalogSettings settings, String groupId, IQuery query, PagingHandler pagingHandler)
   at Dynamicweb.Ecommerce.Indexing.ProductQueryHelper.GetProductsAutoIds(ProductCatalogSettings settings, String groupId, ContentModule contentModule, PageView pageview, IEnumerable`1& facetViewModel, IEnumerable`1& spellCheckerResult)
   at Dynamicweb.Ecommerce.ProductCatalog.ProductCatalogFrontend.RenderProductList(ProductCatalogSettings settings, String groupId, Boolean feed)
   at Dynamicweb.Ecommerce.ProductCatalog.ProductCatalogFrontend.GetContent()
   at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)