title: Symfony2 Choice : Expected argument of type "scalar", "array" given
body: <p>I'm making a form with a choice list. Here's the content of my FormType (only as a test):</p>
  
  <pre><code>$builder-&gt;add('regionUser');
  $builder-&gt;add('roles' ,'choice' ,array('choices' =&gt; array(
          "ROLE_ADMIN" =&gt; "ROLE_ADMIN",
              "ROLE_USER" =&gt; "ROLE_USER",
          ),
          'required'  =&gt; true,
          'multiple' =&gt; false,
  ));
  </code></pre>
  
  <p>When I execute this, I get the following error:</p>
  
  <blockquote>
    <p>Expected argument of type "scalar", "array" given </p>
  </blockquote>
  
  <p>What goes wrong? How to solve it?</p>