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

System.NullReferenceException: Object reference not set to an instance of an object.
   at Co3.Dechra.DVP.Website.Extenders.ProductList.<>c__DisplayClass0_0.b__6(Product p) in C:\Git\Solution\dechra-dvp-website-solution\Dechra.Website\Co3.Dechra.DVP.Website\Extenders\ProductList.cs:line 99
   at System.Linq.EnumerableSorter`2.ComputeKeys(TElement[] elements, Int32 count)
   at System.Linq.EnumerableSorter`1.Sort(TElement[] elements, Int32 count)
   at System.Linq.OrderedEnumerable`1.d__1.MoveNext()
   at Co3.Dechra.DVP.Website.Extenders.ProductList.ExtendTemplate(Template template) in C:\Git\Solution\dechra-dvp-website-solution\Dechra.Website\Co3.Dechra.DVP.Website\Extenders\ProductList.cs:line 99
   at Dynamicweb.Ecommerce.Frontend.Renderer.RenderProductListTemplateExtenders(ProductCollection products, Template template)
   at Dynamicweb.Ecommerce.Frontend.Renderer.RenderProducts(ProductCollection products, Template parentTemplate, String loopName, Int32 loopCounter, Boolean renderRelatedProducts, Boolean renderRelatedLists, Boolean isRecursive, RenderingContext renderingContext)
   at Dynamicweb.Ecommerce.Frontend.Renderer.RenderProductsWithContext(ProductCollection products, Template parentTemplate, RenderingContext renderingContext)
   at Dynamicweb.Ecommerce.Frontend.Renderer.RenderProducts(ProductCollection products)
   at Dynamicweb.Ecommerce.Frontend.Frontend.ListProducts(ProductCollection products, String groupsIdent, Boolean hasBeenSorted)
   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)
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