Fix nullable type hints

Author: cleptric

src/Tracing/HttpClient/TraceableResponseForV5.php

@@ -16,7 +16,7 @@ final class TraceableResponseForV5 extends AbstractTraceableResponse implements
      *
      * @return mixed
      */
-    public function getInfo(string $type = null)
+    public function getInfo(?string $type = null)
     {
         return $this->response->getInfo($type);
     }

tests/End2End/App/Controller/TracingController.php

@@ -21,7 +21,7 @@ class TracingController
      */
     private $connection;
 
-    public function __construct(HubInterface $hub, Connection $connection = null)
+    public function __construct(HubInterface $hub, ?Connection $connection = null)
     {
         $this->hub = $hub;
         $this->connection = $connection;