Fatal error: Uncaught TypeError: Argument 1 passed to Sokil\IsoCodes\Database\Countries::getByAlpha2() must be of the type string, null given, called in /var/www/html/ojs/pages/search/SearchHandler.inc.php on line 272 and defined in /var/www/html/ojs/lib/pkp/lib/vendor/sokil/php-isocodes/src/Database/Countries.php:42 Stack trace: #0 /var/www/html/ojs/pages/search/SearchHandler.inc.php(272): Sokil\IsoCodes\Database\Countries->getByAlpha2() #1 /var/www/html/ojs/lib/pkp/classes/core/PKPRouter.inc.php(395): SearchHandler->authors() #2 /var/www/html/ojs/lib/pkp/classes/core/PKPPageRouter.inc.php(246): PKPRouter->_authorizeInitializeAndCallRequest() #3 /var/www/html/ojs/lib/pkp/classes/core/Dispatcher.inc.php(144): PKPPageRouter->route() #4 /var/www/html/ojs/lib/pkp/classes/core/PKPApplication.inc.php(362): Dispatcher->dispatch() #5 /var/www/html/ojs/index.php(68): PKPApplication->execute() #6 {main} thrown in /var/www/html/ojs/lib/pkp/lib/vendor/sokil/php-isocodes/src/Database/Countries.php on line 42