title: PHP json_decode returns null with Symfony
body: <p>I'm working on REST APIs with Symfony but my json_decode function returns null with my array. I've seen that he can be a probleme with encoding but i'm not sure.
  Here's my json :</p>
  
  <pre><code>{
      "id": 1,
      "title": "Titre",
      "content": "Contenu",
      "vendeur": null
  }
  </code></pre>
  
  <p>Here's my functions to serialize and decode json :</p>
  
  <pre><code>/**
   * @Route("/api_articles_list", name="api_articles_list")
   * @Method({"GET"})
   */
  
  public function showActionListSerialize()
  
  {
  
      $articles =   $this-&gt;getDoctrine()-&gt;getRepository('AppBundle:Article')-&gt;findAll();
  
     // return new JsonResponse(array('articles' =&gt; $articles));
  
      $data =  $this-&gt;get('serializer')-&gt;serialize($articles, 'json');
  
      $response = new Response($data);
  
      $response-&gt;headers-&gt;set('Content-Type', 'application/json');
  
  
      return $response;
  
  
  
  }
  
  /**
   * @Route("/api_articles_list/articles_list", name="articles_list")
   * @Method({"GET"})
   */
  public function showActionList()
  
  {
  
      $articles = json_decode(utf8_encode($this-&gt;showActionListSerialize()), true);
  
      var_dump($articles);
      return $this-&gt;render('listeArticles.html.twig', array('articles' =&gt; $articles));
  
  }
  </code></pre>