title: Doctrine 2 select empty field
body: <p>I'm working on a Symfony 2/Doctrine project that has to use a legacy database. I've created a Doctrine 2 entity form the existing database which generally works just fine. But I can't seem to get one case working: There are some database entries that have empty field (not NULL, just empty) which I want to select via a Doctrine query.</p>
  
  <pre><code>$em = $this-&gt;getDoctrine()-&gt;getManager();
  $query = $em-&gt;createQuery(
      'SELECT p FROM dtrcmsBundle:Page p WHERE p.articleName = :pageName'
  )-&gt;setParameter('pageName', '');
  </code></pre>
  
  <p>Dose not seem to work. Any ideas how to select the empty fields?</p>