code: @JSONField(serialize = false, deserialize = false)
    public String getMentionListString() {
      if (null == this.mentionList) {
        return "";
      }
      StringBuilder builder = new StringBuilder();
      for (int i = 0; i < this.mentionList.size(); i++) {
        builder.append(this.mentionList.get(i));
        if (i != this.mentionList.size() - 1) {
          builder.append(",");
        }
      }
      return builder.toString();
    }
docs: 获取 mention 用户列表的字符串（逗号分隔）
  @return