Registering error handlers in Klein?

Here's my simple TODO app with basic error handling using your
handle_errors decorator:
https://gist.github.com/SamuelMarks/9d7c796b8a336bb556f3

Unfortunately it is always throwing 500s. Is there some other way I'm
meant to be passing errors? E.g.: in Node.js most of my functions have
the signature (err, res).

Thanks for all assistance

PS: The functions from line 103 to 110 was another attempt of mine to
get exceptions handled

PPS: Issue reported 10 days ago - https://github.com/twisted/klein/issues/58