#vulnerable code 
                                @Override
    public void remove(byte[] token) {
        try (Jedis j = pool.getResource()) {
            byte[] tokenKey = toKey(OBS_TKN, token);

            // fetch the observation by token
            byte[] serializedObs = j.get(tokenKey);
            if (serializedObs == null)
                return;

            org.eclipse.californium.core.observe.Observation obs = deserializeObs(serializedObs);
            String registrationId = obs.getRequest().getUserContext().get(CoapRequestBuilder.CTX_REGID);
            Registration registration = getRegistration(j, registrationId);
            String endpoint = registration.getEndpoint();

            byte[] lockValue = null;
            byte[] lockKey = toKey(LOCK_EP, endpoint);
            try {
                lockValue = RedisLock.acquire(j, lockKey);

                unsafeRemoveObservation(j, registrationId, token);
            } finally {
                RedisLock.release(j, lockKey, lockValue);
            }
        }

    } 
                            #location 14 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public void remove(byte[] token) {
        try (Jedis j = pool.getResource()) {
            byte[] tokenKey = toKey(OBS_TKN, token);

            // fetch the observation by token
            byte[] serializedObs = j.get(tokenKey);
            if (serializedObs == null)
                return;

            org.eclipse.californium.core.observe.Observation obs = deserializeObs(serializedObs);
            String registrationId = obs.getRequest().getUserContext().get(CoapRequestBuilder.CTX_REGID);
            Registration registration = getRegistration(j, registrationId);
            if (registration == null) {
                LOG.warn("Unable to remove observation {}, registration {} does not exist anymore", obs.getRequest(),
                        registrationId);
                return;
            }

            String endpoint = registration.getEndpoint();
            byte[] lockValue = null;
            byte[] lockKey = toKey(LOCK_EP, endpoint);
            try {
                lockValue = RedisLock.acquire(j, lockKey);

                unsafeRemoveObservation(j, registrationId, token);
            } finally {
                RedisLock.release(j, lockKey, lockValue);
            }
        }

    }