empty charset fix

[ahorek]

fixes #1299

[ahorek]

the actual problem is in action mailer, that always expects a charset to be defined and #1145 broke it, however I think it should be fixed here, otherwise it'll break older rails versions

@mikel what about add action mailer's tests to travis?

[jeremy]

@ahorek, that's a good idea. Do Action Mailer tests fail with #1145? We could test Action Mailer against Mail master branch as well.

[ahorek]

Do Action Mailer tests fail with #1145?

yes, they do fail. I'm working on CI integration in #1303

[jeremy]

Great! Let's get a PR going in Rails as well. We can track Mail master branch in an additional CI job there.

[jeremy]

How would someone remove the charset now, to rely on default parsing?

This is seeming like something to fix downstream in Action Mailer.

[ahorek]

it isn't just "bad tests", it breaks Action Mailer for real. Even if it'll be fixed in Action Mailer, Mail 2.8 will be incompatible with all previous Rails versions, I think we should avoid that for all costs.

what about skipping blank parameters? https://github.com/mikel/mail/blob/master/lib/mail/fields/parameter_hash.rb#L47

[ahorek]

ok, I fixed that by removing the existing header if you set charset = nil

note that this case didn't work even on previous mail versions including 2.7.1 stable

[ahorek]

if you have time, please review #1308 #1301 these two PRs are preventing a green build on travis

[ahorek]

ping @jeremy

it should be ready, what do you think? any objections? travis build is still failing because of #1308