Better error description when the message body is not set

[calexh-sar]

Created a workflow with a message, and forget to set the payload. I got this error message which didn't point me to the problem. i knoew the throw event errored, but I didn't understand what was "None"

Had to go to Sentry to figure it out - https://sartography.sentry.io/issues/5063127340/?referrer=slack&notification_uuid=2a482806-4238-456e-8eec-6f2b75a67b73&alert_rule_id=12461473&alert_type=issue

And there it becamse clear that the body of the message being sent was evaluating to None.