webman返回json响应头错误

 // 参数验证错误
         if ($exception instanceof ValidateException) {
            return json($exception->getError(), 422);
        }
        if($exception instanceof ApiException){
        //加以下两行也没有用。响应头还是 text/html; charset=UTF-8
            //$response = response();
           // $response->header('Content-Type', 'application/json');
            return json(['code'=>$exception->getCode(),'msg'=>$exception->getMessage()]);
        }
        // 请求异常
        if ($exception instanceof HttpException && request()->isAjax()) {
            return response($exception->getMessage(), $exception->getStatusCode());
        }
        return parent::render($request, $exception);
    }