diff --git a/src/Bundle/ChillMainBundle/Doctrine/ORM/Hydration/FlatHierarchyEntityHydrator.php b/src/Bundle/ChillMainBundle/Doctrine/ORM/Hydration/FlatHierarchyEntityHydrator.php
index 91013ddba..48b6ff875 100644
--- a/src/Bundle/ChillMainBundle/Doctrine/ORM/Hydration/FlatHierarchyEntityHydrator.php
+++ b/src/Bundle/ChillMainBundle/Doctrine/ORM/Hydration/FlatHierarchyEntityHydrator.php
@@ -31,7 +31,7 @@ final class FlatHierarchyEntityHydrator extends ObjectHydrator
     {
         return array_reduce(
             $nodes,
-            static function (array $collect, $node) {
+            static function (array $collect, $node): array {
                 $parentId = (null === $parent = $node->getParent()) ?
                     null :
                     spl_object_id($parent);