Timetable created with empty filename

[Terstorm1029]

Problem:
The Timetable.new() method allows empty filenames to be passed.

Code Used:

campus = Campus(timeout=30, mode="server")
ttdata = campus.api.timetable.new({"filename": "", "start_date": "", "end_date": ""}, {"lessongroups": []})

Result:

{'data': {'created_at': '2026-05-04T08:37:01.725077+00:00', 'end_date': '', 'entries': [], 'filename': '', 'id': 'uid-timetable-d945e402', 'start_date': ''}}