private RaftClientRequest buildRawRequest(
      RaftGroupId groupId, Message message, RaftClientRequest.Type type) throws IOException {
    return RaftClientRequest.newBuilder()
        .setServerId(server.get().getId())
        .setClientId(localFakeId)
        .setCallId(localFakeCallId.incrementAndGet())
        .setGroupId(groupId)
        .setType(type)
        .setMessage(message)
        .build();
  }
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