title: How to keep "empty" selection on my combobox list in JavaFx?
body: <p>In my application I hava combobox which is holding some values from databse ( some real time updated list ). This ComboBox list is updated every 1 minute.
  List dosen't have null values. When I'm setting this list to ComboBox..</p>
  
  <pre><code>ComboBox box = new ComboBox(items);
  </code></pre>
  
  <p>.. there is one extra "empty" row, which is perfectly fine because non value is selected.
  Right after I'm selecting some value my "empty" value disappears from the list. 
  My main question is <strong>How to keep this value on the list?</strong></p>
  
  <p>Why this is a problem.. </p>
  
  <ol>
  <li>Scenerio values is selected in database, first application start
  <ol>
  <li>List is loaded ( wiht selected empty value ).</li>
  <li>Value is selected.</li>
  <li>During first background refresh, empty values disappears, and combobox value is selected to n+1, next value is selected.</li>
  </ol></li>
  <li>If I want to select empty values I have to all clearSelection from selection model / by some extra control.</li>
  </ol>