do not treat empty headers as error?

[rjbs]

Kristopher Matthews wrote at 2013-08-30T12:49:54:

> If $subject is q{}, ->subject() returns undef. The code for subject() in
> Email::Stuffer is:
> 
> $self->{email}->header_str_set(Subject => shift) ? $self : undef;

Seems like a questionable decision that should be reviewed.

[krismatthews]

Per email conversation, I believe rjbs decided to keep this handling as is. :)

[rjbs]

Then I'll close this!