Sorry, I should have said why I changed it.
A user of my webserver tried to use a browser to prototype an AJAX call.
Unfortunately he used GET on a POST-only URL.
The result was a 405 error that displayed the word "None" in the browser which is not a suitable error message.
It originates from the line:

data = None

I changed the method to use the same mechanism as the other error handlers:

message = "method not allowed"

@aaronsw: Do I need to do anything more to support a Pull request?