# File lib/active_record/validations.rb, line 602
      def validates_exclusion_of(*attr_names)
        configuration = { :message => ActiveRecord::Errors.default_error_messages[:exclusion], :on => :save }
        configuration.update(attr_names.pop) if attr_names.last.is_a?(Hash)

        enum = configuration[:in] || configuration[:within]

        raise(ArgumentError, "An object with the method include? is required must be supplied as the :in option of the configuration hash") unless enum.respond_to?("include?")

        validates_each(attr_names, configuration) do |record, attr_name, value|
          record.errors.add(attr_name, configuration[:message]) if enum.include?(value)
        end
      end