#vulnerable code 
                              private BestPossibleStateOutput compute(ClusterEvent event, Map<String, Resource> resourceMap,
      CurrentStateOutput currentStateOutput) {
    ClusterDataCache cache = event.getAttribute(AttributeName.ClusterDataCache.name());
    BestPossibleStateOutput output = new BestPossibleStateOutput();

    HelixManager helixManager = event.getAttribute(AttributeName.helixmanager.name());

    final List<String> failureResources = new ArrayList<>();
    Iterator<Resource> itr = resourceMap.values().iterator();
    while (itr.hasNext()) {
      Resource resource = itr.next();
      boolean result = false;
      try {
        result =
            computeResourceBestPossibleState(event, cache, currentStateOutput, resource, output);
      } catch (HelixException ex) {
        LogUtil.logError(logger, _eventId,
            "Exception when calculating best possible states for " + resource.getResourceName(),
            ex);
      }
      if (!result) {
        failureResources.add(resource.getResourceName());
        LogUtil.logWarn(logger, _eventId,
            "Failed to calculate best possible states for " + resource.getResourceName());
      }
    }

    // Check and report if resource rebalance has failure
    ClusterStatusMonitor clusterStatusMonitor =
        event.getAttribute(AttributeName.clusterStatusMonitor.name());
    updateRebalanceStatus(!failureResources.isEmpty(), helixManager, cache, clusterStatusMonitor,
        "Failed to calculate best possible states for " + failureResources.size() + " resources.");

    return output;
  } 
                            #location 31 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                              private BestPossibleStateOutput compute(ClusterEvent event, Map<String, Resource> resourceMap,
      CurrentStateOutput currentStateOutput) {
    ClusterDataCache cache = event.getAttribute(AttributeName.ClusterDataCache.name());
    BestPossibleStateOutput output = new BestPossibleStateOutput();

    HelixManager helixManager = event.getAttribute(AttributeName.helixmanager.name());
    ClusterStatusMonitor clusterStatusMonitor =
        event.getAttribute(AttributeName.clusterStatusMonitor.name());

    // Check whether the offline/disabled instance count in the cluster reaches the set limit,
    // if yes, pause the rebalancer.
    boolean isValid = validateOfflineInstancesLimit(cache,
        (HelixManager) event.getAttribute(AttributeName.helixmanager.name()));

    final List<String> failureResources = new ArrayList<>();
    Iterator<Resource> itr = resourceMap.values().iterator();
    while (itr.hasNext()) {
      Resource resource = itr.next();
      boolean result = false;
      try {
        result =
            computeResourceBestPossibleState(event, cache, currentStateOutput, resource, output);
      } catch (HelixException ex) {
        LogUtil.logError(logger, _eventId,
            "Exception when calculating best possible states for " + resource.getResourceName(),
            ex);

      }
      if (!result) {
        failureResources.add(resource.getResourceName());
        LogUtil.logWarn(logger, _eventId,
            "Failed to calculate best possible states for " + resource.getResourceName());
      }
    }

    // Check and report if resource rebalance has failure
    updateRebalanceStatus(!isValid || !failureResources.isEmpty(), failureResources, helixManager,
        cache, clusterStatusMonitor,
        "Failed to calculate best possible states for " + failureResources.size() + " resources.");

    return output;
  }