Photo library won't open, can't be repaired
I'm using Photos Version 2.0 (3161.4.140) on a MacBook Air running OS X version 10.12.6 (16G29).
Last time I opened the library successfully was in July or August. When I went to open it yesterday it said "The library could not be opened". Following instructions on the support forums I tried to repair it and got the message "The library “Photos Library.photoslibrary” could not be recognized." and it won't repair the library.
Finder reports the file is 917 bytes...obviously empty. I use Time Machine to back up, but even going back before when the issue occurred, the file is 917 bytes. I've restored several versions anyway, on hope, and none will open and none can be repaired.
I also use Backblaze, and I've restored the oldest version they have, four weeks old, but it too is 917 bytes, can't be opened and can't be repaired.
Any ideas of what else I can try? Any ideas what might have happened?
MacBook Air, macOS Sierra (10.12.6)