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

System.NullReferenceException: Object reference not set to an instance of an object.
   at DanskRideForbund.CustomModules.DistrictModule.DistrictModuleFrontend.<>c.b__3_5(DistrictEntry d) in D:\a\1\s\Application\CustomModules\DistrictModule\DistrictModuleFrontend.cs:line 128
   at System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()
   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
   at System.Linq.OrderedEnumerable`1.d__1.MoveNext()
   at DanskRideForbund.CustomModules.DistrictModule.DistrictModuleFrontend.ShowList(DistrictHelper helper, DataArea dataArea) in D:\a\1\s\Application\CustomModules\DistrictModule\DistrictModuleFrontend.cs:line 128
   at DanskRideForbund.CustomModules.DistrictModule.DistrictModuleFrontend.GetContent() in D:\a\1\s\Application\CustomModules\DistrictModule\DistrictModuleFrontend.cs:line 35
   at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)