code: private CL getFromClusterMap(int clusterId, Map<Integer, CL> clusterMap) {
          CL c = clusterMap.get(clusterId);
          if(c.getFeatureIds() == null) {
              c.setFeatureIds(knowledgeBase.getModelParameters().getFeatureIds()); //fetch the featureIds from model parameters object
          }
          return c;
      }
docs: Always use this method to get the cluster from the clusterMap because it
  ensures that the featureIds are set.
  The featureIds can be unset if we use a data structure which stores
  stuff in file. Since the featureIds field of cluster is transient, the
  information gets lost. This function ensures that it sets it back.
  
  @param clusterId
  @param clusterMap
  @return