title: FOSRestBundle json decode issue
body: <p>Using <a href="https://github.com/FriendsOfSymfony/FOSRestBundle/" rel="nofollow">FOSRestbundle</a>, trying to insert data into table using POST and content-type as <code>application/json</code>. My <code>config.yml</code> has the following </p>
  
  <pre class="lang-yaml prettyprint-override"><code>fos_rest:
    param_fetcher_listener: true
    body_listener: true
    format_listener:
      default_priorities: ['json', html, '*/*']
      prefer_extension: true
    view:
      view_response_listener: force
      failed_validation: HTTP_BAD_REQUEST
      default_engine: php
    formats:
      json: true
  </code></pre>
  
  <p>In controller added something like this</p>
  
  <pre class="lang-php prettyprint-override"><code>$request= $this-&gt;getRequest();
  $form-&gt;bindRequest($request);
  $em = $this-&gt;get('doctrine')-&gt;getEntityManager();
  $em-&gt;persist($entity);
  $em-&gt;flush();
  </code></pre>
  
  <p>But getting <code>null</code> values for all the DB fields.  Any idea?</p>