Slack doesn't accept an empty string in the `text` parameter. However, Nanobot sometimes sends an empty response. This may need a change in the bot's logic as well; still, it should also be handled by the channel. I suggest changing the default message to '<empty_response_from_the_bot>' when the content is empty, so the user will know that the bot was trying to respond with an empty message.
Aleksander W. Oleszkiewicz (Alek)andGitHub