You could try (no subject) in the rule for "Where subject line contains specific words" but unless you know what the body might contain and can narrow it down, you might have all mail with (no subject) deleted -- including that from friends. I have not used Message Rules in several years because MailWasher allows me to be more specific. Perhaps someone who uses OE Message Rules will reply here with a better suggestion.
Some info here:
Windows Insider MVP 2016 -
Microsoft MVP - Consumer Security 2006-2016
Social Media and Community Professional