title: Propel, Filter Column that is blank/empty
body: <p>Im trying to select rows from a table in propel 1.6 where a particular column is blank.</p>
  
  <p>so for example if my query looks like this:</p>
  
  <pre><code>$result = TableQuery::create()
           -&gt;filterByContainer("")
           -&gt;find();
  </code></pre>
  
  <p>I know 100% there are rows where the 'container' column is blank but if I print_r($result) the Propel Collection object has no results.  If I change the query to filter the container column with a particular value e.g 'test' it works fine. </p>
  
  <p>Im sure Im missing something really simple but a google around hasnt give me the answer, neither has the Propel documentation and my attempts at guessing has just caused php fatal errors.</p>
  
  <p>Can anyone point me in the right direction?</p>