mongodb/mongo-ruby-driver — pull request #121 by romanbsd (2012-10-04 22:08:07+00:00)
Title: Serialize ActiveSupport::Multibyte::Chars as String

ActiveSupport::Multibyte::Chars is really a utility class for working with multibyte strings. It can be safely converted serialized as String. The thing is, Rails and especially ActionMailer are using this class all over.