Check for session existence before retrieving it

Calling "getSession()" when no session has been set is deprecated since Symfony 4.1 and will throw an exception in 5.0. Use "hasSession()" instead.

Handler/AbstractExceptionHandler.php

@@ -113,7 +113,8 @@ public function onKernelException(ExceptionEvent $event)
     $backtrace->setFileContent($this->buildBacktrace($event));
 
     // Unset the used session variable
-    $session = $event->getRequest()->getSession();
+    $request = $event->getRequest();
+    $session = $request->hasSession() ? $request->getSession() : null;
     if ($session) {
       $session->remove(self::SESSION_FILENAME);
       $session->set(self::SESSION_ERROR, $exception->getMessage());
@@ -204,7 +205,7 @@ public function onKernelResponse(ResponseEvent $responseObject)
     $response   = $responseObject->getResponse();
     $request    = $responseObject->getRequest();
     $statusCode = $response->getStatusCode();
-    $session    = $request->getSession();
+    $session    = $request->hasSession() ? $request->getSession() : null;
 
     if (!$this->configuration->isProductionEnvironment()) {
       // no production! -> don't sent an email