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System.AggregateException: One or more errors occurred. (Value cannot be null. (Parameter 'source'))
 ---> System.ArgumentNullException: Value cannot be null. (Parameter 'source')
   at System.Linq.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
   at System.Linq.Enumerable.Contains[TSource](IEnumerable`1 source, TSource value, IEqualityComparer`1 comparer)
   at System.Linq.Enumerable.Contains[TSource](IEnumerable`1 source, TSource value)
   at AspNetCore.Views_Partials_grid_editors_DocTypeGridEditor_courseDiscipline.<>c__DisplayClass0_1.<ExecuteAsync>b__2(IPublishedContent x) in C:\inetpub\wwwroot\lipa\Views\Partials\grid\editors\DocTypeGridEditor\courseDiscipline.cshtml:line 28
   at System.Linq.Utilities.<>c__DisplayClass1_0`1.<CombinePredicates>b__0(TSource x)
   at System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()
   at AspNetCore.Views_Partials_grid_editors_DocTypeGridEditor_courseDiscipline.ExecuteAsync() in C:\inetpub\wwwroot\lipa\Views\Partials\grid\editors\DocTypeGridEditor\courseDiscipline.cshtml:line 30
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageCoreAsync(IRazorPage page, ViewContext context)
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageAsync(IRazorPage page, ViewContext context, Boolean invokeViewStarts)
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderAsync(ViewContext context)
   at Microsoft.AspNetCore.Mvc.ViewComponents.ViewViewComponentResult.ExecuteAsync(ViewComponentContext context)
   at Microsoft.AspNetCore.Mvc.ViewComponents.DefaultViewComponentInvoker.InvokeAsync(ViewComponentContext context)
   at Microsoft.AspNetCore.Mvc.ViewComponents.DefaultViewComponentHelper.InvokeCoreAsync(ViewComponentDescriptor descriptor, Object arguments)
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at Our.Umbraco.DocTypeGridEditor.Helpers.DocTypeGridEditorHelper.RenderDocTypeGridEditorItem(IViewComponentHelper helper, IHtmlHelper htmlHelper, IPublishedElement content, String editorAlias, String viewPath, String previewViewPath, Boolean isPreview)
   at Our.Umbraco.DocTypeGridEditor.Helpers.DocTypeGridEditorHelper.RenderDocTypeGridEditorItem(IViewComponentHelper helper, IHtmlHelper htmlHelper, Object model)
   at AspNetCore.app_plugins_doctypegrideditor_render_doctypegrideditor.ExecuteAsync() in C:\inetpub\wwwroot\lipa\app_plugins\doctypegrideditor\render\doctypegrideditor.cshtml:line 4
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageCoreAsync(IRazorPage page, ViewContext context)
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageAsync(IRazorPage page, ViewContext context, Boolean invokeViewStarts)
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderAsync(ViewContext context)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.HtmlHelper.RenderPartialCoreAsync(String partialViewName, Object model, ViewDataDictionary viewData, TextWriter writer)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.HtmlHelper.PartialAsync(String partialViewName, Object model, ViewDataDictionary viewData)
   at AspNetCore.Views_Partials_grid_editors_base.ExecuteAsync() in C:\inetpub\wwwroot\lipa\Views\Partials\grid\editors\base.cshtml:line 11