# File lib/rubytorrent/bencoding.rb, line 142
  def to_bencoding
    "d" + keys.sort.map do |k|
      v = self[k]
      if v.nil?
        nil
      else
        [k.to_bencoding, v.to_bencoding].join
      end
    end.compact.join + "e"
  end