Fix parameter type

With V9 API version, cod_CAEN comes null instead of empty string for government companies (e.g.: 4331473)

Author: robert-stanciu

src/Responses/Info/RetrieveResponseGeneralData.php

@@ -18,7 +18,7 @@ private function __construct(
         public readonly string $document,
         public readonly string $registrationStatus,
         public readonly string $registrationDate,
-        public readonly string $activityCode,
+        public readonly ?string $activityCode,
         public readonly string $bankAccount,
         public readonly bool $roInvoiceStatus,
         public readonly string $authorityName,