Recurring event is set to freq=yearly, but there is no rrule with that

[cyberbeat]

BEGIN:VEVENT
UID:111
DTSTAMP:20181123T192651Z
CATEGORIES;LANGUAGE=de-DE:Party
CONTACT:
DESCRIPTION:xxx
DTSTART;TZID=Europe/Berlin:20160415T210000
DTEND;TZID=Europe/Berlin:20160416T040000
LOCATION:xxx
RDATE;TZID=Europe/Berlin:20161216T210000
RDATE;TZID=Europe/Berlin:20161223T210000
RDATE;TZID=Europe/Berlin:20161230T210000
SEQUENCE:0
SUMMARY:xxx
END:VEVENT

From this event, these dates are generated:
20160415
20161216
20161223
20161230
20170415
20180415
20190415

This is not correct. This problem seems to be the default setting in Freq.php:

protected $rules = ['freq' => 'yearly', 'interval' => 1];

There is no yearly rule in this event.