diff --git a/Classes/S3Storage.php b/Classes/S3Storage.php
index ec24935..9e369eb 100644
--- a/Classes/S3Storage.php
+++ b/Classes/S3Storage.php
@@ -345,7 +345,7 @@ public function getStreamByResourcePath($relativePath)
      * @param callable|null $callback Function called after each iteration
      * @return \Generator<StorageObject>
      */
-    public function getObjects(callable $callback = null)
+    public function getObjects(?callable $callback = null)
     {
         foreach ($this->resourceManager->getCollectionsByStorage($this) as $collection) {
             yield from $this->getObjectsByCollection($collection, $callback);
@@ -360,7 +360,7 @@ public function getObjects(callable $callback = null)
      * @return \Generator<StorageObject>
      * @api
      */
-    public function getObjectsByCollection(CollectionInterface $collection, callable $callback = null)
+    public function getObjectsByCollection(CollectionInterface $collection, ?callable $callback = null)
     {
         $iteration = 0;
         $iterator = $this->resourceRepository->findByCollectionNameIterator($collection->getName());
diff --git a/Classes/S3Target.php b/Classes/S3Target.php
index d41f390..5e6479a 100644
--- a/Classes/S3Target.php
+++ b/Classes/S3Target.php
@@ -242,7 +242,7 @@ public function getAcl()
      * @throws \Neos\Flow\Exception
      * @throws \Exception
      */
-    public function publishCollection(CollectionInterface $collection, callable $callback = null)
+    public function publishCollection(CollectionInterface $collection, ?callable $callback = null)
     {
         $storage = $collection->getStorage();
 
@@ -307,7 +307,7 @@ public function publishCollection(CollectionInterface $collection, callable $cal
      * @param array $potentiallyObsoleteObjects
      * @param callable|null $callback
      */
-    private function publishCollectionFromS3Storage(CollectionInterface $collection, S3Storage $storage, array &$potentiallyObsoleteObjects, callable $callback = null): void
+    private function publishCollectionFromS3Storage(CollectionInterface $collection, S3Storage $storage, array &$potentiallyObsoleteObjects, ?callable $callback = null): void
     {
         foreach ($collection->getObjects($callback) as $object) {
             /** @var StorageObject $object */