Update to Drupal 8.2.6. For more information, see https://www.drupal.org/project/drupal/releases/8.2.6

vendor/symfony/http-foundation/Exception/ConflictingHeadersException.php

@@ -0,0 +1,23 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\HttpFoundation\Exception;
+
+/**
+ * The HTTP request contains headers with conflicting information.
+ *
+ * This exception should trigger an HTTP 400 response in your application code.
+ *
+ * @author Magnus Nordlander <magnus@fervo.se>
+ */
+class ConflictingHeadersException extends \RuntimeException
+{
+}