NullPointerException when importing valid ICS-File (iCAL)

[Timo Stricker]

I checked my ICS File with https://icalendar.org/validator.html and got no Error, just some warnings. 

When I import the ICS File to Confluence Team Calendar I receive the following error messages:

Frontend:

(48e94487-e874-474b-ab9e-14e802cbb57f)\:java.lang.NullPointerException

Log File:

-- referer: http://xx.xx.de/confluence/display/IO/xx | url: /confluence/rest/calendar-services/1.0/calendar/events.json | traceId: f56489657bfe60ff | userName: xx.xx
2020-02-14 14:15:12,308 ERROR [http-nio-8090-exec-4] [extra.calendar3.rest.AbstractResource] getEvents Unable to load events of sub-calendar 3e872c5f-4013-46f1-ac68-fd08725f9b4b

[extra.calendar3.calendarstore.CalendarDataStoreCachingDecorator] load Could not load calendar content from cache key

com.atlassian.confluence.extra.calendar3.exception.CalendarException: calendar3.error.subscription.cannotread

This worked well a time ago!

[Timo Stricker · Accepted solution]

I fixed this via import ICS to Google Calendar and follow ical feed