Problems in Get the last written file from the series of the sub-folders

When a try execute this code in a def, returns: ValueError: max() arg is an empty sequence

But when a execute line by line works The files in directory are xlsx named "YYYY-MM-DD Matinal"

import os
from os.path import getmtime
from pathlib import Path

path_matinal=os.path.abspath(r'C:\Users\garibeiro\Documents')
  
def path():
    directory = Path(path_matinal)
    files = directory.glob('*.xlsx')
    matinal = max(files, key= getmtime)
    print(matinal)