适配 php8

library/think/Loader.php

@@ -613,7 +613,7 @@ class Loader
         if ($type) {
             $name = preg_replace_callback('/_([a-zA-Z])/', function ($match) {
                 return strtoupper($match[1]);
-            }, $name);
+            }, $name ?? '');
 
             return $ucfirst ? ucfirst($name) : lcfirst($name);
         }