static List<String> getStoppedReplicas(ZNRecord znRecord) {
    List<String> stoppedReplicas = znRecord.getListField(ClusterMapUtils.STOPPED_REPLICAS_STR);
    return stoppedReplicas == null ? new ArrayList<>() : stoppedReplicas;
  }
Get the list of stopped replicas on a given instance. This is guaranteed to return a non-null list. It would return
an empty list if there are no stopped replicas or if the field itself is absent for this instance.
@param znRecord the {@link ZNRecord} associated with the interested instance.
@return the list of stopped replicas.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/ClusterMapUtils.java