title: MS Bot to Teams Integration issue
body: <p>We have integrated a bot created in Microsoft Botframeowrk with MS Teams (by publising the channel and adding using App ID). On every message that is sent from Teams to the bot, we are getting an error in the channel logs: "activity must include non empty 'text' field or at least 1 attachment".
  From the console logs, we think that the error is caused by sendActivities being called twice and the second time activity.text field is sent empty which is causing this error. It does not occur in the Web Chat bot. </p>