title: FosRestBundle post/put [create new/update entity] does not read Request correctly
body: <p>long story short:
  Using FOSRestBundle I'm trying to create some entities via POST call, or modify existing via PUT.</p>
  
  <p>here the code:</p>
  
  <pre><code>/**
   * Put action
   * @var Request $request
   * @var integer $id Id of the entity
   * @return View|array
   */
  public function putCountriesAction(Request $request, $id)
  {
      $entity = $this-&gt;getEntity($id);
      $form = $this-&gt;createForm(new CountriesType(), $entity, array('method' =&gt; 'PUT'));
      $form-&gt;bind($request);
  
      if ($form-&gt;isValid()) {
          $em = $this-&gt;getDoctrine()-&gt;getManager();
          $em-&gt;persist($entity);
          $em-&gt;flush();
          return $this-&gt;view(null, Codes::HTTP_NO_CONTENT);
      }
  
      return array(
          'form' =&gt; $form,
      );
  } //[PUT] /countries/{id}
  </code></pre>
  
  <p>If I call /countries/{id} with PUT passing a json like {"description":"Japan"}, it modify my country with id=1, putting an empty description.</p>
  
  <p>If, instead, I try to create a NEW entity with this method:</p>
  
  <pre><code>/**
   * Create new Countries (in batch)
   * @param  Request $request json request
   * @return array           redirect to get_coutry, will show the newly created entities
   */
  public function postCountriesAction(Request $request)
  {
      $entity = new Countries();
      $form = $this-&gt;createForm(new CountriesType(), $entity);
      $form-&gt;bind($request);
  
      if ($form-&gt;isValid()) {
          $em = $this-&gt;getDoctrine()-&gt;getManager();
          $em-&gt;persist($entity);
          $em-&gt;flush();
  
          return $this-&gt;redirectView(
              $this-&gt;generateUrl(
                  'get_country',
                  array('id' =&gt; $entity-&gt;getId())
              ),
              Codes::HTTP_CREATED
          );
      }
  
      return array(
          'form' =&gt; $form,
      );
  } //[PUT {"description":"a_description"}] /countries
  </code></pre>
  
  <p>it gives me an error saying:</p>
  
  <pre><code>exception occurred while executing 'INSERT INTO countries (description) VALUES (?)' with params [null]:
  SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'description' cannot be null
  </code></pre>
  
  <p>so seems that i'm not able to pass correctly the request to bind to the form.</p>
  
  <p>Notice that if i json_decode the request as suggested <a href="https://stackoverflow.com/questions/9304214/manipulating-post-data-to-work-with-symfony2-forms-when-used-in-a-rest-api">here</a> it reply with a </p>
  
  <pre><code>{
      "code":400,
      "message":"Validation Failed",
      "errors":{
          "errors":[
              "This value is not valid."
          ],
          "children":{
              "description":[
              ]
          }
      }
  }
  </code></pre>
  
  <p>Any Advice?</p>
  
  <p>Thanks, 
  Rolls</p>