@Override
  public String getRegionDirFromConsensusGroupId(ConsensusGroupId consensusGroupId) {
    RaftGroupId raftGroupId = Utils.fromConsensusGroupIdToRaftGroupId(consensusGroupId);
    return storageDir + File.separator + raftGroupId.getUuid().toString();
  }
returns the known leader to the given group. NOTICE: if the local peer isn't a member of given
group, getLeader will return null.

@return null if local peer isn't in group, otherwise group leader.
iotdb-core/consensus/src/main/java/org/apache/iotdb/consensus/ratis/RatisConsensus.java