diff --git a/Tests/Units/EntityRepositoryTest.php b/Tests/Units/EntityRepositoryTest.php
index 81c4304..b007923 100644
--- a/Tests/Units/EntityRepositoryTest.php
+++ b/Tests/Units/EntityRepositoryTest.php
@@ -792,8 +792,8 @@ public function testUpdatingInstanceDoesGetDataFromUnitOfWorkWithQueryParam(): v
      * }
      */
     private function getRepository(
-        RestMapping $mapping = null,
-        string $modelName = null,
+        ?RestMapping $mapping = null,
+        ?string $modelName = null,
         bool $mockHydrator = false,
         bool $mockUnitOfWork = false
     ): array {
diff --git a/Tests/Units/Model/SerializerTest.php b/Tests/Units/Model/SerializerTest.php
index e55376d..63d49df 100644
--- a/Tests/Units/Model/SerializerTest.php
+++ b/Tests/Units/Model/SerializerTest.php
@@ -1185,7 +1185,7 @@ private function createNewCartItemDetail(): \Mapado\RestClientSdk\Tests\Model\Js
         return $item;
     }
 
-    private function createNewInstance(Mapping $mapping = null): void
+    private function createNewInstance(?Mapping $mapping = null): void
     {
         $mapping = $mapping ?: $this->getMapping();
         $this->unitOfWork = new UnitOfWork($mapping);