title: symfony2: selected value of choices fields
body: <p>I get something strange with Symfony2 forms. I create a form with a propel entity, values are fine except the "select" (choices) field, that have no selected value.</p>
  
  <p>I tried few tricks like:</p>
  
  <pre><code>$params['choices'] = array('N/A'=&gt; 'N/A');
  $params['data'] = array('N/A');
  $params['preferred_choices'] = array('N/A');
  </code></pre>
  
  <p>Even with this, there is no preselected value. What's wrong ?</p>