handling potential null exception for DropShadowPanel

Author: deltakosh

Microsoft.Toolkit.Uwp.UI.Controls/DropShadowPanel/DropShadowPanel.Properties.cs

@@ -212,47 +212,53 @@ private static void OnBlurRadiusChanged(DependencyObject d, DependencyPropertyCh
         {
             if (IsSupported)
             {
-                ((DropShadowPanel)d).OnBlurRadiusChanged((double)e.NewValue);
+                var panel = d as DropShadowPanel;
+                panel?.OnBlurRadiusChanged((double)e.NewValue);
             }
         }
 
         private static void OnColorChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
         {
             if (IsSupported)
             {
-                ((DropShadowPanel)d).OnColorChanged((Color)e.NewValue);
+                var panel = d as DropShadowPanel;
+                panel?.OnColorChanged((Color)e.NewValue);
             }
         }
 
         private static void OnOffsetXChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
         {
             if (IsSupported)
             {
-                ((DropShadowPanel)d).OnOffsetXChanged((double)e.NewValue);
+                var panel = d as DropShadowPanel;
+                panel?.OnOffsetXChanged((double)e.NewValue);
             }
         }
 
         private static void OnOffsetYChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
         {
             if (IsSupported)
             {
-                ((DropShadowPanel)d).OnOffsetYChanged((double)e.NewValue);
+                var panel = d as DropShadowPanel;
+                panel?.OnOffsetYChanged((double)e.NewValue);
             }
         }
 
         private static void OnOffsetZChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
         {
             if (IsSupported)
             {
-                ((DropShadowPanel)d).OnOffsetZChanged((double)e.NewValue);
+                var panel = d as DropShadowPanel;
+                panel?.OnOffsetZChanged((double)e.NewValue);
             }
         }
 
         private static void OnShadowOpacityChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
         {
             if (IsSupported)
             {
-                ((DropShadowPanel)d).OnShadowOpacityChanged((double)e.NewValue);
+                var panel = d as DropShadowPanel;
+                panel?.OnShadowOpacityChanged((double)e.NewValue);
             }
         }
     }