CherryPy 3: interpreting error messages

I'm stubbing out a method in a nested CherryPy application object. I keep getting error messages of the form

File "/path/to/CherryPy-3.0.2-py2.5.egg/cherrypy/", line 551, in respond
    cherrypy.response.body = self.handler()
File "/path/to/CherryPy-3.0.2-py2.5.egg/cherrypy/", line 24, in __call__
    return self.callable(*self.args, **self.kwargs)
TypeError: 'Data' object is not callable

And the cause? Almost every time, in the browser I've mistyped the URL for my server's Ajax method. I might be invoking foo instead of bar, and the result is always this sort of error message.

Why don't I instead get the old "We didn't find anything"? Dunno. It's probably something in my configuration.