title: Datatrigger on empty string
body: <p>How can a DataTrigger change the visibility of stackpanel, based on a binded string?
  I have the following Xaml</p>
  
  <pre><code>&lt;StackPanel HorizontalAlignment="Right" 
              Orientation="Horizontal" 
              Grid.Column="1"
              Background="#FF7a7a7a"&gt;
      &lt;StackPanel.Style&gt;
          &lt;Style TargetType="{x:Type StackPanel}"&gt;
              &lt;Style.Triggers&gt;
                  &lt;DataTrigger Binding="{Binding SearchText}" Value=""&gt;
                      &lt;Setter Property="Visibility" Value="Hidden"/&gt;
                  &lt;/DataTrigger&gt;
              &lt;/Style.Triggers&gt;
          &lt;/Style&gt;
      &lt;/StackPanel.Style&gt;
      Content....
     &lt;/StackPanel&gt;
  </code></pre>
  
  <p>I Know that <code>SearchText</code> gets updates and binds properly outside the <code>StackPanel</code> </p>
  
  <p>Could somebody point me in the right direction?</p>