@Override
  public Map<String, byte[]> getExtendedAttributes() {
    return extendedAttributes != null
      ? new HashMap<String, byte[]>(extendedAttributes)
      : new HashMap<String, byte[]>();
  }
@return the cluster id on which the change has originated. It there is no such cluster, it
        returns DEFAULT_CLUSTER_ID (cases where replication is not enabled)
hbase-server/src/main/java/org/apache/hadoop/hbase/wal/WALKeyImpl.java