Fatal error: Uncaught Error: Class "APP\handler\Handler" not found in C:\xampp\htdocs\ojs\lib\pkp\controllers\modals\documentLibrary\DocumentLibraryHandler.php:28 Stack trace: #0 {main} thrown in C:\xampp\htdocs\ojs\lib\pkp\controllers\modals\documentLibrary\DocumentLibraryHandler.php on line 28