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

System.NullReferenceException: Object reference not set to an instance of an object.
   at Dynamicweb.Ecommerce.ManufacturerIDValueMapper.MapValues(IEnumerable`1 terms)
   at Dynamicweb.Indexing.Querying.ValueMapperBase.GetMappingsInternal(String fieldId, IEnumerable`1 terms, Boolean includeOccurrences)
   at Dynamicweb.Ecommerce.Indexing.ProductQueryHelper.HandleFieldFacets(Facet facet, FacetGroupResult facets, IIndex index, IQuery query, IList`1 facetResults, Object value, IEnumerable`1 valueMappers)
   at Dynamicweb.Ecommerce.Indexing.ProductQueryHelper.HandleFacetGroupResult(IQuery query, IFacetGroup facetGroup, FacetGroupResult facetGroupResult, IDictionary`2 parameters)
   at Dynamicweb.Ecommerce.Frontend.Frontend.GetProductsFromIndexQuery(ProductCatalogShowType settingsType)
   at Dynamicweb.Ecommerce.Frontend.Frontend.EcomRender()
   at Dynamicweb.Ecommerce.Frontend.Frontend.GetContent()
   at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)