Handles font-size/ line-height shorthand with spaces

Description

While attempting use Premailer to inline CSS for emails originating from Amazon, we started seeing errors when expanding font shorthands that have spaces after the forward slash - e.g font-size/ line-height:

NoMethodError: undefined method `strip' for nil:NilClass
/bundle/gems/css_parser-1.5.0/lib/css_parser/rule_set.rb:99:in `block in each_declaration'
/bundle/gems/css_parser-1.5.0/lib/css_parser/rule_set.rb:97:in `each'
/bundle/gems/css_parser-1.5.0/lib/css_parser/rule_set.rb:97:in `each_declaration'
/bundle/gems/css_parser-1.5.0/lib/css_parser.rb:81:in `block in merge'
/bundle/gems/css_parser-1.5.0/lib/css_parser.rb:69:in `each'
/bundle/gems/css_parser-1.5.0/lib/css_parser.rb:69:in `merge'
...

An example of the email body particulars:

...
a {
    text-decoration: none;
    color: #006699;
    font: 14px/ 16px Arial, sans-serif;
}
...
f_=3Dpe_2640190_232748420_TE_simp_" title=3D"Visit Amazon.com" style=3D"tex=
t-decoration: none; color: rgb(0, 102, 153); font: 14px/ 16px Arial, sans-s=
erif"><img id=3D"amazonLogo" alt=3D"Amazon" src=3D"http://g-ecx.images-amaz=
on.com/images/G/01/x-locale/cs/te/logo.png" style=3D"width: 107px; height: =
31px; border: 0" /></a> </td>=20
...

What it renders like in a browser: amazon_email_example

Tasks

[ ] Any other tests?
[ ] Should a space/spaces be allowed before the /?
[ ] Should some nil safety be added to line 446/447 in rule_set.rb to address TypeError: no implicit conversion of nil into String? (this fix _should address this...)
[ ] Fix failing ruby 1.9.3 test

@grosser, thoughts?

premailer / css_parser

Handles font-size/ line-height shorthand with spaces #89

Description

Tasks