URI::MailTo#to_s

# File tmp/rubies/ruby-3.2.0/lib/uri/mailto.rb, line 239
def to_s
  @scheme + ':' +
    if @to
      @to
    else
      ''
    end +
    if @headers.size > 0
      '?' + @headers.collect{|x| x.join('=')}.join('&')
    else
      ''
    end +
    if @fragment
      '#' + @fragment
    else
      ''
    end
end