MaskedTextBox: fixed Blend designer error.

Main/Source/ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/MaskedTextBox/MaskedTextBox.cs

@@ -141,6 +141,10 @@ namespace Microsoft.Windows.Controls
             if (value == null)
                 value = string.Empty;
 
+            //I have only seen this occur while in Blend, but we need it here so the Blend designer doesn't crash.
+            if (MaskProvider == null) 
+                return value.ToString();
+
             MaskProvider.Set(value.ToString());
             return MaskProvider.ToDisplayString();
         }

Main/Source/ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/Themes/Generic.xaml

@@ -198,7 +198,7 @@
                                 </VisualState>
                             </VisualStateGroup>
                         </VisualStateManager.VisualStateGroups>
-                        <ContentControl x:Name="content" Content="{TemplateBinding Content}" ContentTemplate="{TemplateBinding ContentTemplate}" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}" IsTabStop="False" Focusable="False"/>
+                        <ContentControl x:Name="content" Content="{TemplateBinding Content}" ContentTemplate="{TemplateBinding ContentTemplate}" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"/>
                         <Rectangle x:Name="overlay" Style="{TemplateBinding OverlayStyle}"/>
                         <ContentPresenter x:Name="busycontent">
                             <ContentPresenter.Content>