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

    PriorityQueue<ResourcePriority> resourcePriorityQueue = new PriorityQueue<>();
    TaskDriver taskDriver = null;
    HelixManager helixManager = event.getAttribute(AttributeName.helixmanager.name());
    if (helixManager != null) {
      taskDriver = new TaskDriver(helixManager);
    }
    for (Resource resource : resourceMap.values()) {
      resourcePriorityQueue.add(new ResourcePriority(resource, cache.getIdealState(resource.getResourceName()),
          taskDriver));
    }

    final List<String> failureResources = new ArrayList<>();
    Iterator<ResourcePriority> itr = resourcePriorityQueue.iterator();
    while (itr.hasNext()) {
      Resource resource = itr.next().getResource();
      if (!computeResourceBestPossibleState(event, cache, currentStateOutput, resource, output)) {
        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
    if (!cache.isTaskCache()) {
      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 13 
                            #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());

    final List<String> failureResources = new ArrayList<>();
    Iterator<Resource> itr = resourceMap.values().iterator();
    while (itr.hasNext()) {
      Resource resource = itr.next();
      if (!computeResourceBestPossibleState(event, cache, currentStateOutput, resource, output)) {
        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;
  }