maca/inline-style — pull request #16 by gaiottino (2013-07-05 09:20:00+00:00)
Title: NoMethodError: undefined method `starts_with?' for nil:NilClass

The error occurs when using Pony.

```ruby
Pony.mail({
:to => 'email@domain.com',
:from => 'noreply@domain.com',
:subject => "Testing",
:body => "This is just a test. Ignore it :)",
:via => :smtp,
:via_options => {
:address => 'smtp.gmail.com',
:port => '587',
:enable_starttls_auto => true,
:user_name => 'someone@gmail.com',
:password => 'very_secret',
:authentication => :plain
}
})
```

Just making sure ```part.content_type``` exists before calling ```.starts_with?(m)```