Export donor list from front end fails

ERROR 0 - Call to undefined method Joomla\CMS\Application\SiteApplication::isSite() in /var/www/j4.queerspirit.net/components/com_jdonation/controller/controller.php:250 Call stack # Function Location 1 () JROOT/components/com_jdonation/controller/controller.php:250 2 DonationController->export() JROOT/administrator/components/com_jdonation/libraries/osf/controller/controller.php:302 3 OSFController->execute() JROOT/components/com_jdonation/jdonation.php:35 4 require_once() JROOT/libraries/src/Dispatcher/LegacyComponentDispatcher.php:71 5 Joomla\CMS\Dispatcher\LegacyComponentDispatcher::Joomla\CMS\Dispatcher\{closure}() JROOT/libraries/src/Dispatcher/LegacyComponentDispatcher.php:73 6 Joomla\CMS\Dispatcher\LegacyComponentDispatcher->dispatch() JROOT/libraries/src/Component/ComponentHelper.php:355 7 Joomla\CMS\Component\ComponentHelper::renderComponent() JROOT/libraries/src/Application/SiteApplication.php:200 8 Joomla\CMS\Application\SiteApplication->dispatch() JROOT/libraries/src/Application/SiteApplication.php:241 9 Joomla\CMS\Application\SiteApplication->doExecute() JROOT/libraries/src/Application/CMSApplication.php:294 10 Joomla\CMS\Application\CMSApplication->execute() JROOT/includes/app.php:61 11 require_once() JROOT/index.php:32