#fixed code
                                @Override
    protected ObserveResponse doObserve(final ServerIdentity identity, final ObserveRequest request) {
        final LwM2mPath path = request.getPath();

        // Manage Object case
        if (path.isObject()) {
            List<LwM2mObjectInstance> lwM2mObjectInstances = new ArrayList<>();
            for (LwM2mInstanceEnabler instance : instances.values()) {
                ReadResponse response = instance.observe(identity);
                if (response.isSuccess()) {
                    lwM2mObjectInstances.add((LwM2mObjectInstance) response.getContent());
                }
            }
            return ObserveResponse.success(new LwM2mObject(getId(), lwM2mObjectInstances));
        }

        // Manage Instance case
        final LwM2mInstanceEnabler instance = instances.get(path.getObjectInstanceId());
        if (instance == null)
            return ObserveResponse.notFound();

        if (path.getResourceId() == null) {
            return instance.observe(identity);
        }

        // Manage Resource case
        return instance.observe(identity, path.getResourceId());
    }
#vulnerable code 
                                @Override
    protected ObserveResponse doObserve(final ServerIdentity identity, final ObserveRequest request) {
        final LwM2mPath path = request.getPath();

        // Manage Object case
        if (path.isObject()) {
            List<LwM2mObjectInstance> lwM2mObjectInstances = new ArrayList<>();
            for (Entry<Integer, LwM2mInstanceEnabler> entry : instances.entrySet()) {
                lwM2mObjectInstances.add(getLwM2mObjectInstance(entry.getKey(), entry.getValue(), identity, true));
            }
            return ObserveResponse.success(new LwM2mObject(getId(), lwM2mObjectInstances));
        }

        // Manage Instance case
        final LwM2mInstanceEnabler instance = instances.get(path.getObjectInstanceId());
        if (instance == null)
            return ObserveResponse.notFound();

        if (path.getResourceId() == null) {
            return ObserveResponse
                    .success(getLwM2mObjectInstance(path.getObjectInstanceId(), instance, identity, true));
        }

        // Manage Resource case
        return instance.observe(identity, path.getResourceId());
    } 
                            #location 21 
                            #vulnerability type NULL_DEREFERENCE