title: Why does Doctrine MongoDB ODM always return NULL?
body: <p>I'm having trouble making this work in a fresh install</p>
  
  <pre><code>    /**
       * @Route("/bla")
       * @Template()
       */
      public function blaAction()
      {
          $repository = $this-&gt;get('doctrine.odm.mongodb.document_manager')-&gt;getRepository('CompanySomeBundle:User');
          $user = $repository-&gt;findOneByUsername('bla');
          var_dump($user); // NULL
          return new Response($user-&gt;getUsername()); // Fatal Error, user is not an object
      }
  
      /**
       * @Route("/save-bla")
       */
      public function saveBlaAction()
      {
          $user = new \Company\SomeBundle\Document\User;
          $user-&gt;setUsername('bla');
          $dm = $this-&gt;get('doctrine.odm.mongodb.document_manager');
          $dm-&gt;persist($user);
          $dm-&gt;flush();
          return new Response($user-&gt;getId()); // prints a new ID as expected, but nothing is actually saved to the DB
      }
  </code></pre>
  
  <p>I can't read data that I know is in the DB. And I can't save data either (even though I can get the new generated ID)</p>
  
  <p>Note: PHP's native Mongo works just fine.</p>