diff --git a/typo3/sysext/indexed_search/Classes/Indexer.php b/typo3/sysext/indexed_search/Classes/Indexer.php
index 22a6ab35352833012c7493dd4ba52ead5c21fcdb..a62bcd293c1115a94325e6ea3b303d1b8025cd4e 100644
--- a/typo3/sysext/indexed_search/Classes/Indexer.php
+++ b/typo3/sysext/indexed_search/Classes/Indexer.php
@@ -251,7 +251,7 @@ class Indexer
      * Initializes the object.
      * @param array|null $configuration will be used to set $this->conf, otherwise $this->conf MUST be set with proper values prior to this call
      */
-    public function init(array $configuration = null)
+    public function init(?array $configuration = null)
     {
         if (is_array($configuration)) {
             $this->conf = $configuration;