# File lib/gibbler.rb, line 493
    def __gibbler(digest_type=nil)
      klass = self.class
      value = self.nil? ? "\0" : self.utc.strftime('%Y-%m-%d %H:%M:%S UTC')
      a = Gibbler.digest "%s:%d:%s" % [klass, value.size, value], digest_type
      gibbler_debug klass, a, [klass, value.size, value]
      a
    end