title: Why Symfony2 dont catch exceptions
body: <p>i have a repository</p>
  
  <pre><code>class TurnoRepository extends EntityRepository
  {
      public function findTurnoActivo()
      {
          $q = $this
              -&gt;createQueryBuilder('t')
              -&gt;where('t.activo = :activo')
              -&gt;setParameter('activo', true)
              -&gt;getQuery();
  
          return $q-&gt;getSingleResult();
      }
  }
  </code></pre>
  
  <p>this method throw a NoResultException but if i try to catch in my controller</p>
  
  <pre><code>private function obtenerTurno()
  {
      $em = $this-&gt;getDoctrine()-&gt;getEntityManager();
      $turno = null;
  
      try {
          $turnoActivo = $em-&gt;getRepository('MyBundle:Turno')-&gt;findTurnoActivo();
      } catch (NoResultException $e) {
          return false;
      }
  
      return $turno;
  </code></pre>
  
  <p>}</p>
  
  <p>always i get 500 Internal Server Error on my page</p>