title: Comparing if datetime.datetime exists or None
body: <p>I'm running a small app on Google App Engine with Python.
  In the model I have a property of type DateTimeProperty, which is datetime.datetime. When it's created there is no value (i.e. "None").
  I want compare if that datetime.datetime is None, but I can't.</p>
  
  <pre><code>if object.updated_date is None or object.updated_date &gt;= past:
    object.updated_date = now
  </code></pre>
  
  <p>Both <code>updated_date</code> and <code>past</code> is datetime.datetime.</p>
  
  <p>I get the following error.</p>
  
  <blockquote>
    <p>TypeError: can't compare datetime.datetime to NoneType</p>
  </blockquote>
  
  <p>What is the correct way to do this?</p>