@Override
  public RSGroupInfo getRSGroup(String groupName) throws IOException {
    if (RSGroupInfo.DEFAULT_GROUP.equals(groupName)) {
      return new RSGroupInfo(RSGroupInfo.DEFAULT_GROUP, getOnlineServers());
    } else {
      return null;
    }
  }
A dummy RSGroupInfoManager which only contains a default rs group.
hbase-server/src/main/java/org/apache/hadoop/hbase/rsgroup/DisabledRSGroupInfoManager.java