#vulnerable code 
                             @Override
	public void announce(AnnounceRequestMessage.RequestEvent event,
		boolean inhibitEvents) throws AnnounceException {
		logger.info("Announcing{} to tracker with {}U/{}D/{}L bytes...",
			new Object[] {
				this.formatAnnounceEvent(event),
				this.torrent.getUploaded(),
				this.torrent.getDownloaded(),
				this.torrent.getLeft()
			});

		try {
			ByteBuffer data = null;
			UDPTrackerMessage.UDPTrackerResponseMessage message =
				UDPTrackerMessage.UDPTrackerResponseMessage.parse(data);
			this.handleTrackerResponse(message, inhibitEvents);
		} catch (MessageValidationException mve) {
			logger.error("Tracker message violates expected protocol: {}!",
				mve.getMessage(), mve);
		}
	} 
                            #location 15 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             @Override
	public void announce(AnnounceRequestMessage.RequestEvent event,
		boolean inhibitEvents) throws AnnounceException {
		logger.info("Announcing{} to tracker with {}U/{}D/{}L bytes...",
			new Object[] {
				this.formatAnnounceEvent(event),
				this.torrent.getUploaded(),
				this.torrent.getDownloaded(),
				this.torrent.getLeft()
			});

		try {
			State state = State.CONNECT_REQUEST;
			int tries = 0;

			while (tries <= UDP_MAX_TRIES) {
				if (this.lastConnectionTime != null &&
					new Date().before(this.lastConnectionTime)) {
					state = State.ANNOUNCE_REQUEST;
				}

				tries++;
			}



			ByteBuffer data = null;
			UDPTrackerMessage.UDPTrackerResponseMessage message =
				UDPTrackerMessage.UDPTrackerResponseMessage.parse(data);
			this.handleTrackerResponse(message, inhibitEvents);
		} catch (MessageValidationException mve) {
			logger.error("Tracker message violates expected protocol: {}!",
				mve.getMessage(), mve);
		}
	}