**Symfony version(s) affected**: 4.2.0-BETA1 **Description** Upgrading to Symfony 4.2.0-BETA1 failed with the following error when `framework.session` is set to `false`: ``` In SecurityExtension.php line 70: Warning: array_key_exists() expects parameter 2 to be array, boolean given ``` Looks like it was introduced by https://github.com/symfony/symfony/pull/28446 which doesn't handle the `false` value.