func SignRawTransactionWithKeyAsync(client *rpcclient.Client, tx *wire.MsgTx, privKeysWIF []string) FutureSignRawTransactionWithKeyResult {
	txHex := ""
	if tx != nil {
		buf := bytes.NewBuffer(make([]byte, 0, tx.SerializeSize()))
		if err := tx.Serialize(buf); err != nil {
			responseChan := make(chan *rpcclient.Response, 1)
			responseChan <- &rpcclient.Response{result: nil, err: err} // Can not compile because 'unknown field err in struct literal of type rpcclient.Response'
			return responseChan
		}
		txHex = hex.EncodeToString(buf.Bytes())
	}
	cmd := NewSignRawTransactionKeyCmd(txHex, &privKeysWIF)
	return client.SendCmd(cmd)
}