Add Dedupe Rule allows user to save invalid (empty) RESERVED rule

The 'Add Rule' form generally blocks the user from adding a rule if there are no 'fields' selected. HOWEVER, this form rule fails to catch an empty rule if the user checks 'Reserved'.

This results in a rule which is empty / invalid AND currently can not be deleted.

Fix the form validation so it prevents adding an 'empty' rule (reserved or not).

NOTE: I don't think it makes sense to prevent users with 'administer CiviCRM' from deleting reserved rules. I'll file a separate issue for that.

---- Original Post ----
I've tested the following steps on the CiviCRM Demo...

...I've mistakenly filled in +*no *+fields and that's the message I've got after I've used the rule.

So, if I cannot delete or edit the rule, how can I solve the problem??

After this mistake, I'm not able to add a new inidividual...