I am using paperclip to handle my file uploads, and in one situation I don't want the file to be mandatory. I do however want to make sure it is a specific file type when it is present.

I have this:

class TestModel < ActiveRecord::Base
    #stuff
    has_attached_file :sound #etc...
    validates_attachment_content_type :sound, :content_type => ['audio/mp3', 'application/x-mp3']
end

And when I have no sound file present, it tells me it is not one of the valid content types. I've tried adding '' to the :content_type array, which also doesn't work!

I also attempted creating a lambda procedure for the :if property, but I can't get it to run without some kind of error.

Anything missing here?