How to make a rule check for empty body field

Didn't have much luck turning this info up in my searches.
Our main site publishes nodes automatically using Scheduler and, sometimes, an empty post gets scheduled and overlooked... and posts still empty.
I'd to use Rules to check for empty body when a node is resaved, then do something based on that.
(The do something part is not a big deal. Several options would be suitable).

I just can't seem to find a condition that checks the body for zero text.