500 ERROR when fetching favorite counts for specific user

Reported via accounts.eclipse.org#143 (comment 2957092) by @ddennis.

When visiting their profile, they are getting an unexpected error in the statistics block:

After some investigating, I've noticed that the API is returning a 500 error with the following message in our logs:

ValueError: max(): Argument #1 ($value) must contain at least one element in max() (line 148 of FavoritesController.php).