title: Hide tooltip if binding is null
body: <p>Currently i've got the following code to show a tooltip.</p>
  
  <pre><code>&lt;Border BorderBrush="Black"
          BorderThickness="{Binding Border}"
          Height="23"
          Background="{Binding Color}"&gt;
  &lt;ToolTipService.ToolTip&gt;
      &lt;TextBlock Text="{Binding TooltipInformation}" /&gt;
  &lt;/ToolTipService.ToolTip&gt;
  </code></pre>
  
  <p>This is presented in a ItemsControl with about 25 items. Only a few of these have a value set to <code>TooltipInformation</code></p>
  
  <p>If <code>TooltipInforation</code> is an empty string, it still shows the tooltipbox containing the textblock as a very small window (about 5px high and 20px wide). Even if I set the textblock visbility to collapsed. </p>
  
  <p>Is there a way to completely remove the tooltip if the value of TooltipInformation is null or a empty string?</p>