support nil charset

noticed nil failing when dropping the 772 fix into our mail parser project

@bf4 
The point of the test is to test against passing nil, no matter what the
internal implementation is.
The first part of the test is just to make sure the new encoding did not
get added to ruby / we are actually doing work.

On Sat, Nov 15, 2014 at 9:05 AM, 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
>
> In the implementation you're casting nil.to_s. Encoding.find(nil) raises
> a TypeError, but Encoding.find('') raises an ArgumentError. I'd argue
> that since you're handling the nil case as empty string, your test should
> be empty string, and thus you don't need to affix if from (which I
> generally don't like at the end of long statements)
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/mikel/mail/pull/831/files#r20403513>.
>