Apple Mail rule for BLANK subject lines?

[FloatingBones]

Is there a straightforward way to pattern-match e-mail messages that don't have a subject line? There's no way to put this into an Apple Mail rule. An entry in Apple's discussions recommends an AppleScript, but it's not clear what the rule invoking the script should do. Has anyone figured out how to do this in Apple Mail?

 

[satcomer]

All email servers have that for a long time, not just iCloud email! Also do you know you see your iCloud email all the time by pointing a browser at iCloud.com. You see your email from any browser!

 

[FloatingBones]

All email servers have that for a long time, not just iCloud email! Also do you know you see your iCloud email all the time by pointing a browser at iCloud.com. You see your email from any browser!

I don't see it in iCloud or in the macOS app. Here's the cloud rule screen:

When you attempt to leave the Subject field blank, you get the error "Enter a message subject." It's the same thing in macOS:

If you leave the Subject field blank in macOS, you get an "Invalid Rule" error.

I agree that mail software should have rules for pattern-matching on message, but there's no obvious way to specify a BLANK message. If you do it, what exactly do you have in your rules to do it? A screenshot would be the best way to show this. Thanks.