Factory reset DS220+ without drives

I've recently switched from my DS220+ to a dedicated SFF server and am now looking to resell the NAS. I've just tried booting it up to factory reset it and learned that it doesn't actually allow you to do anything without a drive (both of which I've already installed in the new server). Now I'm wondering: Do I need to reinsert a drive in order to factory reset it? Or is everything I would want to reset already gone because it was stored on my drives? https://finds.synology.com/# does show the DSM version so there seems to be some form of internal storage.