The previous owner might have cut it out to make room for the parking/clearance light.
I don't think there's much you can do unless you want to fill it in yourself or get new headlights.
EDIT: the headlights may have come like that as well.
EDIT #2: after looking at a few eBay aftermarket headlights, i noticed they come with a cutout hole like that for the parking/clearance light.
Last edited by plebsaur; Feb 20, 2018 4:41pm.