#vulnerable code 
                                @Override
    protected void calcRemainingQuota(Long quota, Long refreshInterval,
                                      Long requestTime, String key, Rate rate) {
        if (quota != null) {
            String quotaKey = key + QUOTA_SUFFIX;
            handleExpiration(quotaKey, refreshInterval, rate);
            long usage = requestTime != null ? requestTime : 0L;
            Long current = 0L;
            try {
                current = this.redisTemplate.boundValueOps(quotaKey).increment(usage);
            } catch (RuntimeException e) {
                String msg = "Failed retrieving rate for " + quotaKey + ", will return quota limit";
                rateLimiterErrorHandler.handleError(msg, e);
            }
            rate.setRemainingQuota(Math.max(-1, quota - current));
        }
    } 
                            #location 15 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    protected void calcRemainingQuota(Long quota, Long refreshInterval,
                                      Long requestTime, String key, Rate rate) {
        if (Objects.nonNull(quota)) {
            String quotaKey = key + QUOTA_SUFFIX;
            long usage = requestTime != null ? requestTime : 0L;
            Long remaining = calcRemaining(quota, refreshInterval, usage, quotaKey, rate);
            rate.setRemainingQuota(remaining);
        }
    }