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