PHP Deprecation: Implicitly marking parameter $menu_names as nullable is deprecated

Error:
PHP Deprecated: Drupal\responsive_menu\Form\SettingsForm::getMenuOptions(): Implicitly marking parameter $menu_names as nullable is deprecated, the explicit nullable type must be used instead in /web/modules/contrib/responsive_menu/src/Form/SettingsForm.php on line 407

protected function getMenuOptions(array $menu_names = NULL) {

Fix:
protected function getMenuOptions(?array $menu_names = NULL) {