title: Image control default image binding at XAML page when retrieve image url is empty
body: <p>Hi All
      At Silverlight 4.0 XAML page (not using code behind), I'm binding Source to Image control. I want to show default image when retrival ImageUrl (from Database) is null or empty.</p>
  
  <p>I'm trying the TargetNullValue as following , but not showing default image when ImageUrl is null or empty</p>
  
  <pre><code>     &lt;Image Grid.Column="0"
                 x:Name="YourAvator"
                 Width="100"
                 Height="100"
                 Source="{Binding Path=ImageUrl, Mode=OneWay, TargetNullValue='../Images/default_avator.jpg'}"
                 Stretch="Fill" /&gt;
  </code></pre>
  
  <p>Please advise me.</p>
  
  <p>Thanks.</p>