diff --git a/Tests/Fixtures/CustomArrayObject.php b/Tests/Fixtures/CustomArrayObject.php
index 4ca7f4a99..7bc850ddc 100644
--- a/Tests/Fixtures/CustomArrayObject.php
+++ b/Tests/Fixtures/CustomArrayObject.php
@@ -19,7 +19,7 @@ class CustomArrayObject implements \ArrayAccess, \IteratorAggregate, \Countable,
 {
     private $array;
 
-    public function __construct(array $array = null)
+    public function __construct(?array $array = null)
     {
         $this->array = $array ?: [];
     }