from RFC5545 (p. 54) https://datatracker.ietf.org/doc/html/rfc5545#page-54 For cases where a "VEVENT" calendar component specifies a "DTSTART" property with a DATE value type but no "DTEND" nor "DURATION" property, the event's duration is taken to be one day. Fix https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/327