code: public static Message buildNewLeader(long epoch) {
      NewLeader nl = NewLeader.newBuilder().setEpoch(epoch).build();
      return Message.newBuilder().setType(MessageType.NEW_LEADER)
                                 .setNewLeader(nl)
                                 .build();
    }
docs: Creates a NEW_LEADER message.
  
  @param epoch the established epoch.
  @return a protobuf message.