#vulnerable code 
                             public void run() {
		log.info("ProactiveGcTask starting, oldGenOccupancyFraction:" + oldGenOccupancyFraction + ", datetime: "
				+ new Date());
		try {
			oldMemoryPool = getOldMemoryPool();
			long maxOldBytes = getMemoryPoolMaxOrCommitted(oldMemoryPool);
			long oldUsedBytes = oldMemoryPool.getUsage().getUsed();
			log.info(String.format("max old gen: %.2f MB, used old gen: %.2f MB, available old gen: %.2f MB.",
					SizeUnit.BYTES.toMegaBytes(maxOldBytes), SizeUnit.BYTES.toMegaBytes(oldUsedBytes),
					SizeUnit.BYTES.toMegaBytes(maxOldBytes - oldUsedBytes)));
			if (needTriggerGc(maxOldBytes, oldUsedBytes, oldGenOccupancyFraction)) {
				preGc();
				doGc();
				postGc();
			}
		} catch (Exception e) {
			log.error(e.getMessage(), e);
		} finally {
			if (!scheduler.isShutdown()) { // reschedule this task
				try {
					scheduler.reschedule(this);
				} catch (Exception e) {
					log.error(e.getMessage(), e);
				}
			}
		}
	} 
                            #location 6 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             public void run() {
		logger.info("ProactiveGcTask starting, oldGenOccupancyFraction:" + oldGenOccupancyFraction);
		try {
			long usedOldBytes = logOldGenStatus();

			if (needTriggerGc(maxOldBytes, usedOldBytes, oldGenOccupancyFraction)) {
				preGc();
				doGc();
				postGc();
			}
		} catch (Exception e) {
			logger.error(e.getMessage(), e);
		} finally {
			scheduler.reschedule(this);
		}
	}