title: Empty String Check in Trigger
body: <p>How can I check for an empty string in a trigger?</p>
  <pre><code>&lt;Trigger Property=&quot;Source&quot; SourceName=&quot;ControlName&quot;  Value=&quot;&quot;&gt;
       &lt;Setter Property=&quot;Height&quot; Value=&quot;0&quot; TargetName=&quot;ControlName&quot; /&gt;
  &lt;/Trigger&gt;
  </code></pre>
  <p>I have set the Height of the Control to 0 if the source of the imageControl is empty string or not set? How can I do it, Basically If the image is not set then I want to hide the image control in the template.</p>