code: public void addMembers(final List<String> memberIds, final AVIMConversationCallback callback) {
      if (null == memberIds || memberIds.size() < 1) {
        if (null != callback) {
          callback.done(new AVIMException(new IllegalArgumentException("memberIds is null")));
        }
        return;
      }
      Map<String, Object> params = new HashMap<String, Object>();
      params.put(Conversation.PARAM_CONVERSATION_MEMBER, memberIds);
      boolean ret = InternalConfiguration.getOperationTube().processMembers(this.client.getClientId(), this.conversationId,
              getType(), JSON.toJSONString(params), Conversation.AVIMOperation.CONVERSATION_ADD_MEMBER, callback);
      if (!ret && null != callback) {
        callback.internalDone(null,
                new AVException(AVException.OPERATION_FORBIDDEN, "couldn't start service in background."));
      }
    }
docs: 在聊天对话中间增加新的参与者
  
  @param memberIds
  @param callback
  @since 3.0