refactor: add workaround for old Config\App file

Author: kenjis

system/HTTP/RequestTrait.php

@@ -66,6 +66,11 @@ public function getIPAddress(): string
         // @phpstan-ignore-next-line
         $proxyIPs = $this->proxyIPs ?? config(App::class)->proxyIPs;
         // @phpstan-ignore-next-line
+
+        // Workaround for old Config\App file. App::$proxyIPs may be empty string.
+        if ($proxyIPs === '') {
+            $proxyIPs = [];
+        }
         if (! empty($proxyIPs) && (! is_array($proxyIPs) || is_int(array_key_first($proxyIPs)))) {
             throw new ConfigException(
                 'You must set an array with Proxy IP address key and HTTP header name value in Config\App::$proxyIPs.'