title: How do I set up a NSPredicate to look for objects that have a nil attribute
body: <p>I have a <code>ManagedObject class</code>, and one of the members of the class is a <code>NSDate</code>.  I would like to display all objects of the class for which the date is NOT set.  I tried using a predicate like this:</p>
  
  <pre><code>NSPredicate *predicate = [NSPredicate predicateWithFormat: @"(date = NIL)"];
  </code></pre>
  
  <p>But I still get objects where the <code>date</code> is set.  What is the right way to set up a predicate for this?</p>