diff --git a/src/Bundle/ChillPersonBundle/Export/Aggregator/PersonAggregators/CountryOfBirthAggregator.php b/src/Bundle/ChillPersonBundle/Export/Aggregator/PersonAggregators/CountryOfBirthAggregator.php
index 27191d21f..897cac14a 100644
--- a/src/Bundle/ChillPersonBundle/Export/Aggregator/PersonAggregators/CountryOfBirthAggregator.php
+++ b/src/Bundle/ChillPersonBundle/Export/Aggregator/PersonAggregators/CountryOfBirthAggregator.php
@@ -36,7 +36,7 @@ final readonly class CountryOfBirthAggregator implements AggregatorInterface, Ex
         return null;
     }
 
-    public function alterQuery(QueryBuilder $qb, $data)
+    public function alterQuery(QueryBuilder $qb, $data): void
     {
         // add a clause in select part
         if ('country' === $data['group_by_level']) {
@@ -139,7 +139,7 @@ final readonly class CountryOfBirthAggregator implements AggregatorInterface, Ex
             ];
         }
 
-        return static fn (string $value): string => $labels[$value];
+        return static fn (?string $value): string => $labels[(string) $value];
     }
 
     public function getQueryKeys($data)