code: func (msg *PssMsg) serialize() []byte {
  	rlpdata, _ := rlp.EncodeToBytes(struct {
  		To      []byte
  		Payload *whisper.Envelope
  	}{
  		To:      msg.To,
  		Payload: msg.Payload,
  	})
  	return rlpdata
  }
docs: // serializes the message for use in cache