This shouldnt need to be final

src/Plugin/Field/FieldType/DateRecurFieldItemList.php

@@ -22,7 +22,7 @@ use Symfony\Component\EventDispatcher\EventDispatcherInterface;
  *
  * @method \Drupal\date_recur\Plugin\Field\FieldType\DateRecurItem|null first()
  */
-final class DateRecurFieldItemList extends DateRangeFieldItemList {
+class DateRecurFieldItemList extends DateRangeFieldItemList {
 
   /**
    * Value for 'default_time_zone_source' to get time zone from a fixed string.