I solved problem with "Undefined index: _route" as follows. I changed line 121 in '/src/PrestaShopBundle/Controller/Admin/CommonController.php' file to:
// $routeName = $request->attributes->get('caller_route', $request->attributes->get('caller_parameters', ['_route' => false])['_route']);
$routeN1 = $request->attributes->get('caller_parameters', ['_route' => false]);
if (!isset($routeN1['_route'])) {
$routeN1['_route'] = false;
}
$routeName = $request->attributes->get('caller_route', $routeN1['_route']);