node.js-无法通过Slack API发布消息-获取错误“no_text”

为什么我会收到错误“no_text”？

下面的Json是有效的，取自slack文档示例。

在里面bot.postMessage(channel, '', params)如果我填充第二个参数（即用“some_text”替换“”），它会打印“some_text”，但没有附件。

bot.postMessage(channel, 'some_text', params)-->工作正常，但附件没有出现。

    const element = {
      "text": "Would you like to play a game?",
      "response_type": "in_channel",
      "attachments": [
          {
              "text": "Choose a game to play",
              "fallback": "If you could read this message, you'd be choosing something fun to do right now.",
              "color": "#3AA3E3",
              "attachment_type": "default",
              "callback_id": "game_selection",
              "actions": [
                  {
                      "name": "games_list",
                      "text": "Pick a game...",
                      "type": "select",
                      "options": [
                          {
                              "text": "Hearts",
                              "value": "hearts"
                          },
                          {
                              "text": "Global Thermonuclear War",
                              "value": "war"
                          }
                      ]
                  }
              ]
          }
      ]
  }

    console.log('JSON.stringify(element): '+JSON.stringify(element));
    params = {
      icon_emoji: ':r2:',
      attachments: JSON.stringify(element)
    }
    bot.postMessage(channel, '', params).always(function (data) {...}