Fatal error: Uncaught Error: Using $this when not in object context in E:\code\yqhswz\core\ThinkPHP\Library\Vendor\mpdf\includes\upperCase.php:2
Stack trace:
#0 {main}
thrown in E:\code\yqhswz\core\ThinkPHP\Library\Vendor\mpdf\includes\upperCase.php on line 2