code: func (n *Node) doRaftLeader(conn redcon.Conn, cmd redcon.Command) (interface{}, error) {
  	if len(cmd.Args) != 1 {
  		return nil, ErrWrongNumberOfArguments
  	}
  	leader := n.raft.Leader()
  	if leader == "" {
  		conn.WriteNull()
  	} else {
  		conn.WriteBulkString(leader)
  	}
  	return nil, nil
  }
docs: // doRaftLeader handles a "RAFTLEADER" client command.