# File lib/grape/validations/validators/exactly_one_of.rb, line 13
      def message(default_key = nil)
        options = instance_variable_get(:@option)
        if options_key?(:message)
          (options_key?(default_key, options[:message]) ? options[:message][default_key] : options[:message])
        else
          default_key
        end
      end