output: #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);
  		}
  	}
input: #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