iCal Export: cannot instanciate abstract interface 'net.fortuna.ical4j.util.UidGenerator'

Failed to execute the [groovy] macro. Cause: [startup failed:
xwiki:MoccaiCalendar.Service: 75: You cannot create an instance from the abstract interface 'net.fortuna.ical4j.util.UidGenerator'.
 @ line 75, column 23.
       UidGenerator ug = new UidGenerator(new SimpleHostInfo('atelier-medias.org'), eventDocument.documentReference.toString());
                         ^1 error