title: How to add empty option in select in AngularJS?
body: <p>I have a select box.</p>
  
  <p>When no value is selected, I have the empty option <code>--</code>. It's OK !</p>
  
  <p>Once an option is selected, the empty option disappears. </p>
  
  <p>But I would like that it is always there to have the opportunity to choose <code>--</code>. </p>
  
  <p>Is it possible ? </p>
  
  <pre><code>&lt;select ng-model="project" ng-options="act.id as act.name for act in actors"&gt;&lt;/select&gt;
  </code></pre>