# File lib/grape/validations/validators/default.rb, line 9
      def validate_param!(attr_name, params)
        return if params.key? attr_name
        params[attr_name] = if @default.is_a? Proc
                              @default.call
                            elsif @default.frozen? || !duplicatable?(@default)
                              @default
                            else
                              duplicate(@default)
                            end
      end