title: How to specify null value as filter in a Doctrine query?
body: <p>I am using Doctrine 1.1 in Zend. I am trying to write a query that will return records that have a null value in a certain column.</p>
  
  <pre><code>    $q = Doctrine_Query::create()
      -&gt;select('a.*')
      -&gt;from('RuleSet a')
      -&gt;where('a.vertical_id = ?', null);
  
      $ruleset_names_result = $q-&gt;execute(array(), Doctrine::HYDRATE_ARRAY);
  </code></pre>
  
  <p>I have three records in the ruleset table which have a <em>NULL</em> value in the vertical_id column yet the query doest not find these.</p>
  
  <p>Appreciate the help.</p>
  
  <p>Sid.</p>