I created a filter to match any of a long list of email domains. ("Companies" trying to offer me loans, daily.) The filter is set up to "match any." The list tests "From ends with." I accidentally added another row but forgot to enter a domain in the empty field. That filter row matched ALL my email, (and sent them to my trash).
I think it would be a wise user design feature to reject any rows that have a blank field. 🙂