html5rocks/www.html5rocks.com — pull request #574 by tmatsuo (2013-08-21 07:14:36+00:00)
Title: Fix a KeyError when there's no User-Agent header field

I happened to find 500 errors for requests without the User-Agent header field. I apologize that I have not tested this code. I'd appreciate it if anyone could run a test before merging. Thanks.