title: How to do generic queries with Objectify, to get a sample entity of each Kind
body: <p>I have many different Kinds in my app, they are unrelated in the Datastore, but they share a common Java base class which helps me process them generically.   (By generically I mean without regard to their kind, not in the Java 'generics' sense.)</p>
  
  <p>Now I want to perform some tests on one entity from each kind, and I can't figure out how to do it.</p>
  
  <p>I want to do something like this:</p>
  
  <pre><code>Class&lt;? extends MyBaseUnit&gt; cl = getNextKind();
  MyBaseUnit bu = (MyBaseUnit) ofy().load().type( cl ).filter( ?? ).first().now();
  </code></pre>
  
  <p>I don't think there is any such thing as a null filter, and if I just remove the filter() call then first() returns a Ref and I can't seem to do much with that.  </p>
  
  <p>I guess I could use a filter of ("id >", 0) for all the kinds with a long id, but what would a similar meaningless filter be for the ones with a string name?</p>
  
  <p>Or maybe there is a better way of doing this?  My ideal would be to retrieve a different entity every time I run the test.</p>