fix: payload is null when encounter 5xx error [SPMVP-7314]

Author: bepsvpt

src/Requests/Request.php

@@ -105,7 +105,7 @@ protected function request(
 
         if (! $response->successful()) {
             $this->toException(
-                $payload,
+                $payload ?: new stdClass(),
                 $response->body(),
                 $response->status(),
             );