diff --git a/src/ResponseBuilder.php b/src/ResponseBuilder.php
index f03c96e..1a36e98 100644
--- a/src/ResponseBuilder.php
+++ b/src/ResponseBuilder.php
@@ -40,7 +40,7 @@ public function __construct(protected DataFormatterInterface $dataFormatter, pro
     {
     }
 
-    public function buildErrorResponse(ServerRequestInterface $request, int $code, Throwable $error = null): ResponsePlusInterface
+    public function buildErrorResponse(ServerRequestInterface $request, int $code, ?Throwable $error = null): ResponsePlusInterface
     {
         $body = new SwooleStream($this->formatErrorResponse($request, $code, $error));
         return $this->response()->addHeader('content-type', 'application/json')->setBody($body);
@@ -67,7 +67,7 @@ protected function formatResponse($response, ServerRequestInterface $request): s
         return $this->packer->pack($response);
     }
 
-    protected function formatErrorResponse(ServerRequestInterface $request, int $code, Throwable $error = null): string
+    protected function formatErrorResponse(ServerRequestInterface $request, int $code, ?Throwable $error = null): string
     {
         [$code, $message] = $this->error($code, $error?->getMessage());
         $response = $this->dataFormatter->formatErrorResponse(