I can't access to admin panel
I have this error when I'm trying to go on the admin panel:
Une erreur s'est produite
0 Call to undefined method Joomla\CMS\Application\AdministratorApplication::isAdmin()
Call stack
Function Location
1 () JROOT/plugins/system/helixultimate/helixultimate.php:135
2 plgSystemHelixultimate->onAfterRoute() JROOT/libraries/src/Plugin/CMSPlugin.php:285
3 Joomla\CMS\Plugin\CMSPlugin->Joomla\CMS\Plugin{closure}() JROOT/libraries/vendor/joomla/event/src/Dispatcher.php:486
4 Joomla\Event\Dispatcher->dispatch() JROOT/libraries/src/Application/EventAware.php:111
5 Joomla\CMS\Application\WebApplication->triggerEvent() JROOT/libraries/src/Application/AdministratorApplication.php:547
6 Joomla\CMS\Application\AdministratorApplication->route() JROOT/libraries/src/Application/AdministratorApplication.php:171
7 Joomla\CMS\Application\AdministratorApplication->doExecute() JROOT/libraries/src/Application/CMSApplication.php:278
8 Joomla\CMS\Application\CMSApplication->execute() JROOT/administrator/includes/app.php:63
9 require_once() JROOT/administrator/index.php:32