#vulnerable code 
                                private Long calcRemaining(Long limit, Long refreshInterval, long usage,
                               String key, Rate rate) {
        rate.setReset(SECONDS.toMillis(refreshInterval));
        Long current = 0L;
        try {
            current = redisTemplate.opsForValue().increment(key, usage);
            // Redis returns the value of key after the increment, check for the first increment, and the expiration time is set
            if (current != null && current.equals(usage)) {
                handleExpiration(key, refreshInterval);
            }
        } catch (RuntimeException e) {
            String msg = "Failed retrieving rate for " + key + ", will return the current value";
            rateLimiterErrorHandler.handleError(msg, e);
        }
        return Math.max(-1, limit - current);
    } 
                            #location 15 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                private Long calcRemaining(Long limit, Long refreshInterval, long usage,
                               String key, Rate rate) {
        rate.setReset(SECONDS.toMillis(refreshInterval));
        Long current = 0L;
        try {
            current = redisTemplate.opsForValue().increment(key, usage);
            // Redis returns the value of key after the increment, check for the first increment, and the expiration time is set
            if (current != null && current.equals(usage)) {
                handleExpiration(key, refreshInterval);
            }
        } catch (RuntimeException e) {
            String msg = "Failed retrieving rate for " + key + ", will return the current value";
            rateLimiterErrorHandler.handleError(msg, e);
        }
        return Math.max(-1, limit - (current != null ? current : 0L));
    }