# File lib/rmail/header.rb, line 177
    def fetch(name, *rest)
      if rest.length > 1
        raise ArgumentError, "wrong # of arguments(#{rest.length + 1} for 2)"
      end
      result = self[name]
      if result.nil?
        if block_given?
          yield name
        elsif rest.length == 1
          rest[0]
        else
          raise IndexError, 'name not found'
        end
      else
        result
      end
    end