Greg, I think this code will work just fine for non-change objects too. Can you give it a try.
In my case, I wanted to capture the comments and assign them to a workflow variable, "detailedChangeDescription". But if you're not interested in that, you can possibly try something like this:
wt.workflow.work.WfAssignedActivity activity = (wt.workflow.work.WfAssignedActivity) self.getObject();
wt.workflow.engine.ProcessData actData = activity.getContext();
if (actData.getTaskComments().length() < 10) { throw new wt.util.WTException(new Throwable(new String("Hey user - please type something into the Comments field!")));
}
Of course you can adjust the quantity of characters it looks for too, based on your need. I wanted the user to enter at least 10 characters. Therefore .length() < 10. You can change that if you wish.