diff --git a/src/Bundle/ChillMainBundle/Doctrine/ORM/Hydration/FlatHierarchyEntityHydrator.php b/src/Bundle/ChillMainBundle/Doctrine/ORM/Hydration/FlatHierarchyEntityHydrator.php
index eaa7b6c72..91013ddba 100644
--- a/src/Bundle/ChillMainBundle/Doctrine/ORM/Hydration/FlatHierarchyEntityHydrator.php
+++ b/src/Bundle/ChillMainBundle/Doctrine/ORM/Hydration/FlatHierarchyEntityHydrator.php
@@ -18,8 +18,7 @@ final class FlatHierarchyEntityHydrator extends ObjectHydrator
 
     private function flatListGenerator(array $hashMap, ?int $parent = null): Generator
     {
-        $parent ??= spl_object_id($parent);
-
+        $parent = null === $parent ? null : spl_object_id($parent);
         $hashMap += [$parent => []];
 
         foreach ($hashMap[$parent] as $node) {