title: FOSElastica why my result is not serialized?
body: <p>I have configured <code>FOSElasticaBundle</code> as follow:</p>
  
  <pre><code>fos_elastica:
      clients:
          default: { host: %elasticsearch_host%, port: %elasticsearch_port%  }
      serializer: ~
      indexes:
          app:
              types:
                  tags:
                      serializer:
                          groups: [Default]
                      mappings:
                          name: ~
                      persistence:
                          driver: orm
                          model: AppBundle\Entity\Tag
                          provider: ~
                          listener: ~
                          finder: ~
  </code></pre>
  
  <p>To my test i have three tags in my database: <code>tag1</code>, <code>tag2</code>, <code>new tag</code>.
  My entity looks like:</p>
  
  <pre><code>namespace AppBundle\Entity;
  
  use Doctrine\ORM\Mapping as ORM;
  use Symfony\Component\Validator\Constraints as Assert;
  
  /**
   * Class Tag
   * @package AppBundle\Entity
   *
   * @ORM\Entity
   * @ORM\Table(name="tags")
   */
  class Tag
  {
      /**
       * @ORM\Id
       * @ORM\Column(type="integer")
       * @ORM\GeneratedValue(strategy="AUTO")
       * @var int
       */
      protected $id;
  
      /**
       * @var string
       * @ORM\Column(type="string")
       * @Assert\NotBlank()
       */
      protected $name;
  </code></pre>
  
  <p>I am searching indexed tags as follows:</p>
  
  <pre><code>$finder = $this-&gt;container-&gt;get('fos_elastica.finder.app.tags');
  
  $results = [];
  if ($query !== null) {
      $results = $finder-&gt;find("*" . $query . "*");
  
      //$results should be serialized, but aren't
  
      return new Response($results);
  }
  
  return new JsonResponse([
      'results' =&gt; $results
  ]);
  </code></pre>
  
  <p>And my response is: <code>{"results":[{},{},{}]}</code></p>
  
  <p>Why <code>$results</code> are not serialized ? When I debug <code>$results</code> there are objects inside.</p>