System.NullReferenceException: Object reference not set to an instance of an object.
   at ASP._Page_app_plugins_unibase_grideditors_mediaitemlist_Render_cshtml.Execute() in A:\meng.de-Shoperweiterung\Web.App\app_plugins\unibase\grideditors\mediaitemlist\Render.cshtml:line 58
   at System.Web.WebPages.WebPageBase.ExecutePageHierarchy()
   at System.Web.Mvc.WebViewPage.ExecutePageHierarchy()
   at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage)
   at Umbraco.Web.Mvc.ProfilingView.Render(ViewContext viewContext, TextWriter writer)
   at System.Web.Mvc.Html.PartialExtensions.Partial(HtmlHelper htmlHelper, String partialViewName, Object model, ViewDataDictionary viewData)
   at ASP._Page_Views_Partials_grid_editors_Base_cshtml.Execute() in A:\meng.de-Shoperweiterung\Web.App\Views\Partials\grid\editors\Base.cshtml:line 20