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

System.NullReferenceException: Object reference not set to an instance of an object.
   at Dynamicweb.Ecommerce.Products.GroupService._Closure$__51-0._Lambda$__0(Group g)
   at Dynamicweb.Ecommerce.Products.GroupService.FindPath(Shop fromShop, Group toGroup)
   at Bluedesk.NotificationSubscribers.ForceProductOnArea.OnNotify(String notification, NotificationArgs args) in C:\vso\KoksGroup\KoksGroup\NotificationSubscribers\KoksGroup.Notifications\ForceProductOnArea.cs:line 38
   at Dynamicweb.Extensibility.Notifications.NotificationManager.Notify(String notification, NotificationArgs eventArgs)
   at Dynamicweb.Ecommerce.Frontend.Frontend.RenderProduct(Product product, String unitId)
   at Dynamicweb.Ecommerce.Frontend.Frontend.EcomRender()
   at Dynamicweb.Ecommerce.Frontend.Frontend.GetContent()
   at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)