set explicit nullable parameters for PHP 8.4

Author: jorgsowa

src/Endpoint/ContainerAttachWebsocket.php

@@ -27,7 +27,8 @@ public function getExtraHeaders(): array
         );
     }
 
-    protected function transformResponseBody(ResponseInterface $response, SerializerInterface $serializer, string $contentType = null)
+    protected function transformResponseBody(ResponseInterface $response, SerializerInterface $serializer, ?string
+    $contentType = null)
     {
         if (200 === $response->getStatusCode() && DockerRawStream::HEADER === $contentType) {
             return new AttachWebsocketStream($response->getBody());

src/Endpoint/ContainerLogs.php

@@ -11,7 +11,7 @@
 
 class ContainerLogs extends BaseEndpoint
 {
-    protected function transformResponseBody(ResponseInterface $response, SerializerInterface $serializer, string $contentType = null)
+    protected function transformResponseBody(ResponseInterface $response, SerializerInterface $serializer, ?string $contentType = null)
     {
         if (200 === $response->getStatusCode() && DockerRawStream::HEADER === $contentType) {
             return new DockerRawStream($response->getBody());