# File lib/apipie/validator.rb, line 447
      def self.build(param_description, argument, options, block)
        # in Ruby 1.8.x the arity on block without args is -1
        # while in Ruby 1.9+ it is 0
        self.new(param_description, block, options[:param_group]) if block.is_a?(Proc) && block.arity <= 0 && argument == Array
      end