PerlDancer/Dancer2 — pull request #505 by b10m (2013-11-13 10:26:07+00:00)
Title: Fixed empty HTTP_REFERER calls.

When HTTP_REFERER is not set (which is a quite likely scenario), dancer
would die with:
isa check for "referer" failed: undef is not a string!

This forces request->referer to return an empty string, rather than
undef (which is not a Str).