Empty tile warning details; definitely what you would expect if there's not a catastrophic error, but you're getting blank tiles.
such as: ```
MBTiles error, serving empty { Error: SQLITE_CORRUPT: database disk image is malformed
lily_tile_server | at Error (native) errno: 11, code: 'SQLITE_CORRUPT' }
```
https://github.com/klokantech/tileserver-gl/issues/323
