title: Converter visible when empty
body: <p>How can I make a converter VisibleWhenEmptyString. I did it as below but it does not work. Regards</p>
  
  <pre><code>    &lt;converters:ValueWhenConverter x:Key="VisibleWhenEmptyString"&gt;
      &lt;converters:ValueWhenConverter.When&gt;
          &lt;x:String &gt;&lt;/x:String&gt;
      &lt;/converters:ValueWhenConverter.When&gt;
      &lt;converters:ValueWhenConverter.Value&gt;
          &lt;Visibility&gt;Visible&lt;/Visibility&gt;
      &lt;/converters:ValueWhenConverter.Value&gt;
      &lt;converters:ValueWhenConverter.Otherwise&gt;
          &lt;Visibility&gt;Collapsed&lt;/Visibility&gt;
      &lt;/converters:ValueWhenConverter.Otherwise&gt;
  &lt;/converters:ValueWhenConverter&gt;
  </code></pre>