title: Call to a member function has() on null symfony2
body: <p>I have 5 class Categoria, Produto, Subcategoria, Subproduto and Comanda and for execute search in all classes i try make a service like:</p>
  
  <pre>
  namespace AppBundle\Controller;
  
  
  use Symfony\Bundle\FrameworkBundle\Controller\Controller;
  
  class AccessClassController extends Controller{
  
      /**
       * Retorna todas as categorias ativas
       */
      public function CategoriasAtivasAction()
      {
          $em = $this->getDoctrine()->getManager();
  
          $categorias = $em->getRepository('AppBundle:Categoria')->findByAtivo(1);
  
          return $categorias;
      }
  }
   </pre>
  
  <p>And i try access the service on ComandaController</p>
  
  <pre>
  class ComandaController extends Controller
  {
  ...
  public function newAction(Request $request, $id)
      {
          $comanda = new Comanda();
  
          $categorias = $this->get('categorias.ativas')->CategoriasAtivasAction();
  ...
  </pre>
  
  <p>Then symfony return error</p>
  
  <p><code>
  Call to a member function has() on null
  500 Internal Server Error - FatalThrowableError
  </code></p>
  
  <p>My services.yml has</p>
  
  <pre>
  
  services:
    categorias.ativas:
       class: AppBundle\Controller\AccessClassController
  
  </pre>
  
  <p>Whats wrong?</p>