Empty lookup value validated even when use_puppet_default is checked
Since https://github.com/theforeman/foreman/blob/develop/app/models/lookup_value.rb#L10 was added
adding a matcher with an empty value isn't possible even when checking use_puppet_default.
Workaround for now: put any value, save the smart class parameter, edit it again and check use puppet default.
Fixes #11663 - Empty lookup value not validated when use_puppet_default is checked