diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0b505ec..1eaabbc 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -14,9 +14,14 @@ jobs:
       matrix:
         php-versions: ['7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3']
         coverage: ['xdebug']
+        code-style: ['no']
         code-analysis: ['no']
         include:
           - php-versions: '7.1'
+            code-style: 'yes'
+            code-analysis: 'yes'
+          - php-versions: '8.4'
+            code-style: 'no'
             code-analysis: 'yes'
     steps:
       - name: Checkout
@@ -45,7 +50,7 @@ jobs:
         run: composer install --no-progress --prefer-dist --optimize-autoloader
 
       - name: Code Analysis (PHP CS-Fixer)
-        if: matrix.code-analysis == 'yes'
+        if: matrix.code-style == 'yes'
         run: php vendor/bin/php-cs-fixer fix --dry-run --diff
 
       - name: Code Analysis (PHPStan)
diff --git a/lib/Client.php b/lib/Client.php
index 0837e8d..ed07045 100644
--- a/lib/Client.php
+++ b/lib/Client.php
@@ -175,7 +175,7 @@ public function send(RequestInterface $request): ResponseInterface
      * After calling sendAsync, you must therefore occasionally call the poll()
      * method, or wait().
      */
-    public function sendAsync(RequestInterface $request, callable $success = null, callable $error = null)
+    public function sendAsync(RequestInterface $request, ?callable $success = null, ?callable $error = null)
     {
         $this->emit('beforeRequest', [$request]);
         $this->sendAsyncInternal($request, $success, $error);
diff --git a/lib/Response.php b/lib/Response.php
index c06c963..7b622fe 100644
--- a/lib/Response.php
+++ b/lib/Response.php
@@ -103,7 +103,7 @@ class Response extends Message implements ResponseInterface
      * @param array      $headers
      * @param resource   $body
      */
-    public function __construct($status = 500, array $headers = null, $body = null)
+    public function __construct($status = 500, ?array $headers = null, $body = null)
     {
         if (null !== $status) {
             $this->setStatus($status);