fix: php8.4 Deprecated: Implicitly marking parameter $key as nullable is deprecated

src/Config.php

@@ -27,7 +27,7 @@ class Config
         getConfig as traitGetConfig;
     }
 
-    public function getConfig(string $key = null, mixed $default = null): mixed
+    public function getConfig(string|null $key = null, mixed $default = null): mixed
     {
         if ($key == 'merchant_no') {
             return $this->getConfig('sub_merchant_list')[0]['merchant_no'];

src/Service/TransactionService.php

@@ -62,7 +62,7 @@ class TransactionService
         string             $payOrderNo = '',
         string             $settleType = '',
         string             $remark = '',
-        TradeAccBusiFields $accBusiFields = null,
+        ?TradeAccBusiFields $accBusiFields = null,
     ): object {
         $request = new TransPreorderRequest();