[Bug] X- properties cannot be parsed in jcal although their type is properly set.

[niccokunzmann]

Describe the bug

To reproduce

from icalendar import Calendar, vPeriod
import datetime
calendar = Calendar()
date_range = vPeriod([datetime.datetime(2025, 2, 2), datetime.datetime(2025, 2, 3)])
calendar["x-filter-date-range"] = date_range
jcal = calendar.to_jcal()
calendar2 = Calendar.from_jcal(jcal)  

Output:

icalendar.error.JCalParsingError: [1][2][3] in vUnknown: The value must be a string. Got value: ['2025-02-02T00:00:00', '2025-02-02T00:00:00']

Expected behavior

We should be able to parse this as we know which type we expect.
I would like a vPeriod in there.

Environment

• Operating system: Linux
• Python version: 3.13
• icalendar version: 7.0.1

Additional context

• I tested it with the latest version. For example, I used the command pip3 install --upgrade https://github.com/collective/icalendar.git.
• I attached the .ics sample file, or there is no .ics sample file.

See also:

• Support jCal output format (RFC7265) waldbaer/icalendar-events-cli#42 (comment)