String ackId = headers.get(Stomp.Headers.Ack.ACK_ID);
if (ackId == null && this.version.equals(Stomp.V1_2)) {
throw new ProtocolException("NACK received without an ack header to acknowledge!");
}
TransactionId activemqTx = null;
String stompTx = headers.get(Stomp.Headers.TRANSACTION);
if (stompTx != null) {
activemqTx = transactions.get(stompTx);
if (activemqTx == null) {
throw new ProtocolException("Invalid transaction id: " + stompTx);