static List<String> getSealedReplicas(ZNRecord znRecord) {
    List<String> sealedReplicas = znRecord.getListField(ClusterMapUtils.SEALED_STR);
    return sealedReplicas == null ? new ArrayList<>() : sealedReplicas;
  }
Get the list of sealed replicas on a given instance. This is guaranteed to return a non-null list. It would return
an empty list if there are no sealed 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 sealed replicas.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/ClusterMapUtils.java