Fixed empty HTTP_REFERER calls.

[b10m]

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).

[veryrusty]

@b10m nice pickup on the behaviour of those request object attributes when their corresponding request header doesn't exist!

I'm wondering why you elected to return an empty string vs altering the data type on those accessors?
( i.e. define them as isa => Maybe[Str] to allow for the possibility of undef values )

[b10m]

I needed a quick hack and didn't know about Maybe[Str]. I don't really have a strong preference either way, as long as the bug gets killed.

[veryrusty]

My preference would be for changing the type on those attributes. That way Request->referer and Request->headers->header('Referer') are consistent. @b10m do you want to do another pull request?

[b10m]

You make a solid point. Code patched and pushed.

[veryrusty]

Looks good. It's a 👍 from me..

[xsawyerx]

👍 Good work!

[xsawyerx]

Merged, thanks! :)