private void migrateHFileRefs(ZKReplicationQueueStorageForMigration oldQueueStorage)
    throws Exception {
    MigrationIterator<Pair<String, List<String>>> iter = oldQueueStorage.listAllHFileRefs();
    for (;;) {
      Pair<String, List<String>> pair = iter.next();
      if (pair == null) {
        return;
      }
      if (peers.containsKey(pair.getFirst())) {
        queueStorage.batchUpdateHFileRefs(pair.getFirst(), pair.getSecond());
      }
    }
  }
For replication peer cluster key or endpoint class, null and empty string is same. So here
don't use {@link StringUtils#equals(CharSequence, CharSequence)} directly.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/replication/ReplicationPeerManager.java