diff --git a/.github/workflows/pr-validation.yml b/.github/workflows/pr-validation.yml
index eb004ee5..65bdc31c 100644
--- a/.github/workflows/pr-validation.yml
+++ b/.github/workflows/pr-validation.yml
@@ -18,7 +18,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php-versions: ['7.4', '8.1', '8.2', '8.3']
+        php-versions: ['7.4', '8.1', '8.2', '8.3', '8.4']
     steps:
     - uses: actions/checkout@v4.2.2
     - name: Setup PHP
diff --git a/src/GraphClientFactory.php b/src/GraphClientFactory.php
index d61520b7..91383142 100644
--- a/src/GraphClientFactory.php
+++ b/src/GraphClientFactory.php
@@ -143,7 +143,7 @@ public static function createWithMiddleware(HandlerStack $handlerStack): Client
      * @param callable|null $handler final handler
      * @return HandlerStack
      */
-    public static function getDefaultHandlerStack(callable $handler = null): HandlerStack
+    public static function getDefaultHandlerStack(?callable $handler = null): HandlerStack
     {
         $handlerStack = parent::getDefaultHandlerStack();
         if ($handler) {
diff --git a/src/Requests/BaseBatchRequestBuilder.php b/src/Requests/BaseBatchRequestBuilder.php
index 0cea36fa..c3cc3634 100644
--- a/src/Requests/BaseBatchRequestBuilder.php
+++ b/src/Requests/BaseBatchRequestBuilder.php
@@ -46,7 +46,7 @@ class BaseBatchRequestBuilder
      * @param RequestAdapter $requestAdapter
      * @param array<string, array{class-string<T>, string}>|null $errorMappings
      */
-    public function __construct(RequestAdapter $requestAdapter, array $errorMappings = null)
+    public function __construct(RequestAdapter $requestAdapter, ?array $errorMappings = null)
     {
         $this->requestAdapter = $requestAdapter;
         $this->errorMappings = $errorMappings;