Fixed implicitly nullable params (#6616)

Author: huangdijia

src/CoreMiddleware.php

@@ -90,7 +90,7 @@ protected function transferToResponse($response, ServerRequestInterface $request
         return $this->responseBuilder->buildResponse($request, $response);
     }
 
-    protected function buildErrorData(ServerRequestInterface $request, int $code, string $message = null, Throwable $throwable = null): array
+    protected function buildErrorData(ServerRequestInterface $request, int $code, ?string $message = null, ?Throwable $throwable = null): array
     {
         $id = $request->getAttribute(Constant::REQUEST_ID);
 

src/TcpServer.php

@@ -61,7 +61,7 @@ public function __construct(
         ExceptionHandlerDispatcher $exceptionDispatcher,
         ProtocolManager $protocolManager,
         StdoutLoggerInterface $logger,
-        string $protocol = null
+        ?string $protocol = null
     ) {
         parent::__construct($container, $dispatcher, $exceptionDispatcher, $logger);