In all e-mails and documents, the placeholders are printed out with the placeholder text if there is no value in the database. It should be SPACES not something like [LAST_NAME]. That looks like crap in a notification to customers.
Yes. I agree that we should have it empty. However, if you don't use that field, I think it is better that you go to Events Booking -> Emails & Messages, find that tag and remove it. That would be best