Skip rendering unknown popup element types

Author: dotMorten

src/Toolkit/Toolkit/UI/Controls/PopupViewer/PopupElementItemsControl.Windows.cs

@@ -26,6 +26,8 @@ namespace Esri.ArcGISRuntime.Toolkit.Primitives
     /// </summary>
     public partial class PopupElementItemsControl : ItemsControl
     {
+        private static DataTemplate UnsupportedPopupElementTemplate = new DataTemplate();
+
         /// <inheritdoc />
         protected override void PrepareContainerForItemOverride(DependencyObject element, object item)
         {
@@ -59,6 +61,10 @@ protected override void PrepareContainerForItemOverride(DependencyObject element
                     // always returned as TextPopupElement.
                     Debug.Assert(false);
                 }
+                else
+                {
+                    presenter.ContentTemplate = UnsupportedPopupElementTemplate; // Renders empty / skips
+                }
             }
         }
 

src/Toolkit/Toolkit/UI/Controls/PopupViewer/PopupElementTemplateSelector.Maui.cs

@@ -33,7 +33,8 @@ public class PopupElementTemplateSelector : DataTemplateSelector
         private static DataTemplate DefaultMediaPopupElementTemplate;
         private static DataTemplate DefaultFieldsPopupElementTemplate;
         private static DataTemplate DefaultAttachmentsPopupElementTemplate;
-        
+        private static DataTemplate UnsupportedPopupElementTemplate;
+
         static PopupElementTemplateSelector()
         {
             DefaultTextPopupElementTemplate = new DataTemplate(() =>
@@ -61,6 +62,10 @@ static PopupElementTemplateSelector()
                 view.SetBinding(AttachmentsPopupElementView.ElementProperty, Binding.SelfPath);
                 return view;
             });
+            UnsupportedPopupElementTemplate = new DataTemplate(() =>
+            {
+                return new Grid() { IsVisible = false };
+            });
         }
 
         /// <summary>
@@ -104,7 +109,7 @@ protected override DataTemplate OnSelectTemplate(object item, BindableObject ele
                 // always returned as TextPopupElement.
                 Debug.Assert(false);
             }
-            return new DataTemplate();
+            return UnsupportedPopupElementTemplate;
         }
 
         /// <summary>