People Calendars created before version 1.1.0 that contain deleted users do not load

java.lang.IllegalArgumentException: Argument not a net.fortuna.ical4j.model.Property
	at net.fortuna.ical4j.model.PropertyList.add(PropertyList.java:141)
	at net.fortuna.ical4j.model.PropertyList.add(PropertyList.java:129)
	at com.atlassian.confluence.extra.calendar3.calendarstore.PeopleCalendarDataStore$1.transform(PeopleCalendarDataStore.java:315)
	at com.atlassian.confluence.extra.calendar3.calendarstore.PeopleCalendarDataStore.getSubCalendarContent(PeopleCalendarDataStore.java:296)
	at com.atlassian.confluence.extra.calendar3.calendarstore.PeopleCalendarDataStore.getSubCalendarContent(PeopleCalendarDataStore.java:65)
	at com.atlassian.confluence.extra.calendar3.calendarstore.CalendarDataStoreCachingDecorator.getSubCalendarContentFromCalendarDataStore(CalendarDataStoreCachingDecorator.java:265)
	at com.atlassian.confluence.extra.calendar3.calendarstore.CalendarDataStoreCachingDecorator.getSubCalendarContent(CalendarDataStoreCachingDecorator.java:207)
	at com.atlassian.confluence.extra.calendar3.calendarstore.DelegatingCalendarDataStore.getSubCalendarContent(DelegatingCalendarDataStore.java:144)
	at com.atlassian.confluence.extra.calendar3.DefaultCalendarManager.getEvents(DefaultCalendarManager.java:451)