support nil charset

noticed nil failing when dropping the 772 fix into our mail parser project

@bf4 
Damn :D

Fixed!

On Sun, Nov 16, 2014 at 8:08 PM, Benjamin Fleischer <
notifications@github.com> wrote:

> In spec/mail/encoding_spec.rb:
>
> >        }.each do |from, to|
> >          it "should support #{from}" do
> > -          expect { ::Encoding.find(from) }.to raise_error(ArgumentError)
> > +          expect { ::Encoding.find(from) }.to raise_error(ArgumentError) if from
>
> Just remove the if from here and I'll merge it
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/mikel/mail/pull/831/files#r20417981>.
>