Here is a link to the latest guidance re parents from the DFE.
Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: Cannot perform runtime binding on a null reference at CallSite.Target(Closure , CallSite , Object ) at System.Dynamic.UpdateDelegates.UpdateAndExecute1[T0,TRet](CallSite site, T0 arg0) at CallSite.Target(Closure , CallSite , Object ) at ASP._Page_app_plugins_documentpicker_documentpicker_cshtml.Execute() in c:\inetpub\vhosts\west-borough.kent.sch.uk\httpdocs\App_Plugins\DocumentPicker\documentpicker.cshtml:line 11 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 System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance) at System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer) at Umbraco.Core.Profiling.ProfilingView.Render(ViewContext viewContext, TextWriter writer) at System.Web.Mvc.HtmlHelper.RenderPartialInternal(String partialViewName, ViewDataDictionary viewData, Object model, TextWriter writer, ViewEngineCollection viewEngineCollection) at System.Web.Mvc.Html.PartialExtensions.Partial(HtmlHelper htmlHelper, String partialViewName, Object model, ViewDataDictionary viewData) at System.Web.Mvc.Html.PartialExtensions.Partial(HtmlHelper htmlHelper, String partialViewName, Object model) at ASP._Page_Views_Partials_grid_editors_base_cshtml.Execute() in c:\inetpub\vhosts\west-borough.kent.sch.uk\httpdocs\Views\Partials\Grid\Editors\Base.cshtml:line 20