2.1.13 [RFC5546] Section 3.2.1, PUBLISH-Type iCalendar Objects MUST Contain One or More VEVENT Components

The table in [RFC5546] contains a value of "1+" in the Presence column for the VEVENT component.

Outlook can export an iCalendar object with a method of PUBLISH that has no VEVENT components when the user exports a calendar or calendar range containing no appointments.