It all depends on the definition of empty. I take a practical approach: if there isn't someone sleeping in that unit regularly, it is empty. If I walk my dog

It all depends on the definition of empty. I take a practical approach: if there isn't someone sleeping in that unit regularly, it is empty. If I walk my dog through a neighborhood and see countless dark/cold apartments, ones where nobody has seen a light turn on in years and the mail either piles up or has been stopped, those are empty. Others take different approaches. Some are of the view that a unit is not empty so long as it is listed as someone's "primary residence", irrespective of whether they actually sleep there.