Synchronization::getSlaveEvents

private function getSlaveEvents(Event $event): CoreBaseMap
{
	$map = $this->getEventExceptionsMap($event);

	return new CoreEventEventMap(
		array_reduce($map->getCollection(), static function ($result, $value)
		{
			/** @var Event $value */
			if ($value->getOriginalDateFrom())
			{
				$key = $value->getOriginalDateFrom()->format('Ymd');
				$result[$key] = $value->getId();
			}

			return $result;
		}, []) ?? []
	);
}