Serialize twice

gistfile1.txt

My controller:

/**
* @ParamConverter("channel", class="ApiBundle:Channel")
*/
public function showAction(Channel $channel, Request $request)
    {
    	$serializer = $this->container->get('serializer');
	$channel = $serializer->serialize($channel, 'json', SerializationContext::create()->setGroups(array('list')));
		
	$view = $this->view($channel, 200);
	return $this->handleView($view);
    }

My Entity:

class Channel
{
    /**
     * @var integer $id
     * @Groups({"list", "details"})
     *
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

     /** 
     * @Groups({"list"})
     * @var string $nombre
     * @ORM\Column(name="nombre", type="string", length=255)
     */
    private $nombre;