diff --git a/Api/ReindexInterface.php b/Api/ReindexInterface.php
index 1f56da8..a68a6e5 100644
--- a/Api/ReindexInterface.php
+++ b/Api/ReindexInterface.php
@@ -17,5 +17,5 @@ interface ReindexInterface
     /**
      * @param array|null $indexIds
      */
-    public function reindex(array $indexIds = null) : void;
+    public function reindex(?array $indexIds = null) : void;
 }
diff --git a/Api/StrategyInterface.php b/Api/StrategyInterface.php
index d11789d..56a4f13 100644
--- a/Api/StrategyInterface.php
+++ b/Api/StrategyInterface.php
@@ -17,5 +17,5 @@ interface StrategyInterface
     /**
      * @param array|null $indexIds
      */
-    public function process(array $indexIds = null) : void;
+    public function process(?array $indexIds = null) : void;
 }
diff --git a/Model/Reindex.php b/Model/Reindex.php
index 2ca1e52..9f70e08 100644
--- a/Model/Reindex.php
+++ b/Model/Reindex.php
@@ -29,7 +29,7 @@ public function __construct(IndexerFactory $indexerFactory)
      *
      * @param array|null $indexIds
      */
-    public function reindex(array $indexIds = null) : void
+    public function reindex(?array $indexIds = null) : void
     {
         foreach ($indexIds as $index) {
             $indexer = $this->indexerFactory->create();
diff --git a/Model/Strategies/Deferred.php b/Model/Strategies/Deferred.php
index 2c45a9f..cda89c6 100644
--- a/Model/Strategies/Deferred.php
+++ b/Model/Strategies/Deferred.php
@@ -32,7 +32,7 @@ public function __construct(PublisherInterface $publisher)
      *
      * @param array|null $indexIds
      */
-    public function process(array $indexIds = null) : void
+    public function process(?array $indexIds = null) : void
     {
         $this->publisher->publish(self::TOPIC_NAME, $indexIds);
     }
diff --git a/Model/Strategies/Standard.php b/Model/Strategies/Standard.php
index b0bafe2..8199fc6 100644
--- a/Model/Strategies/Standard.php
+++ b/Model/Strategies/Standard.php
@@ -30,7 +30,7 @@ public function __construct(Reindex $reindexService)
      *
      * @param array|null $indexIds
      */
-    public function process(array $indexIds = null) : void
+    public function process(?array $indexIds = null) : void
     {
         $this->reindexService->reindex($indexIds);
     }
diff --git a/Model/Strategy.php b/Model/Strategy.php
index 82ad2bb..ba07233 100644
--- a/Model/Strategy.php
+++ b/Model/Strategy.php
@@ -27,7 +27,7 @@ public function __construct(StrategyResolver $resolver)
      * @param array|null $indexIds
      * @throws \Magento\Framework\Exception\InputException
      */
-    public function process(array $indexIds = null) : void
+    public function process(?array $indexIds = null) : void
     {
         $this->resolver->resolveActive()->process($indexIds);
     }