add: if (!itemToDelete) { return; } 
context:     deleteOccurrence: function (aOccurrence) {        var itemToDelete = getOccurrenceOrParent(aOccurrence);        if (!itemToDelete.parentItem.hasSameIds(itemToDelete)) {            var event = itemToDelete.parentItem.clone();            event.recurrenceInfo.removeOccurrenceAt(itemToDelete.recurrenceId);            doTransaction('modify', event, event.calendar, itemToDelete.parentItem, null);        } else {            doTransaction('delete', itemToDelete, itemToDelete.calendar, null, null);        }    }
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/3a7e5a014cbc8b0e799d298ce758b55e758c3fc8/calendar-views.js/clean/calendar/base/content/calendar-views.js