RichTextBox: fixed bug when using RichTextBox and not data binding to the Text Property

ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/RichTextBox/RichTextBox.cs

@@ -113,6 +113,8 @@ namespace Microsoft.Windows.Controls
         {
             Binding binding = BindingOperations.GetBinding(this, TextProperty);
 
+            if (binding != null)
+            {
                 if (binding.UpdateSourceTrigger == UpdateSourceTrigger.Default || binding.UpdateSourceTrigger == UpdateSourceTrigger.LostFocus)
                 {
                     LostFocus += (o, ea) => UpdateText(); //do this synchronously
@@ -122,6 +124,7 @@ namespace Microsoft.Windows.Controls
                     TextChanged += (o, ea) => InvokeUpdateText(); //do this async
                 }
             }
+        }
 
         #endregion //Event Hanlders
     }