private void forceStepDownLeader(RaftGroup group) throws Exception {
    // when newLeaderPeerId == null, ratis forces current leader to step down and raise new
    // election
    transferLeader(group, null);
  }
NOTICE: transferLeader *does not guarantee* the leader be transferred to newLeader.
iotdb-core/consensus/src/main/java/org/apache/iotdb/consensus/ratis/RatisConsensus.java