use persistent collection to get groups

src/Domain/User/User.php

@@ -7,6 +7,7 @@ use JsonSerializable;
 use Doctrine\ORM\Mapping as ORM;
 use DateTime;
 use App\Domain\Group\Group ;
+use Doctrine\ORM\PersistentCollection;
 
 /**
  * @ORM\Entity
@@ -134,9 +135,9 @@ class User implements JsonSerializable
     }
 
     /**
-     * @return array
+     * @return PersistentCollection
      */
-    public function getGroups(): array
+    public function getGroups(): PersistentCollection
     {
         return $this->groups;
     }