Following the 3.x tutorial on 4.x alpha 3 - "Exception: Df2Controller handler class cannot be loaded"

trying to construct the index controller, getting

"Exception: Df2Controller handler class cannot be loaded"

I'm guessing this is a change? I'd really rather not downgrade to 3.4, does anyone know how to fix?

thanks

EDITED TO ADD

I appear to have solved it, but I have no idea how.

Change try { $response = $application->handle($SERVER['REQUEST_URI']);

to:

try { $response = $application->handle(1);