`find_single`: should we raise `FileNotFoundError`?

[mathause]

filefisher/filefisher/_filefinder.py

Line 182 in 42d0239

def find_single(self, keys=None, **keys_kwargs) -> "FileContainer":

More correct but not consistent (I mean if you want to catch the error [but you can of course do a except (FileNotFoundError, ValueError)]).