thinkphp集成swoole报错Uncaught think\exception\ErrorException: Swoole\Http\Response::write(): data to send is empty in

thinkphp5.1集成swoole使用命令： php think swoole之后

报错信息：

[think\exception\ErrorException]
Uncaught think\exception\ErrorException: Swoole\Http\Response::write(): data to send is empty in /usr/local/nginx/html/exam/vendor/topthink/think-swoole/src/Ap
plication.php:122
Stack trace:
#0 [internal function]: think\Error::appError(2, 'Swoole\\Http\\Res...', '/usr/local/ngin...', 122, Array)
#1 /usr/local/nginx/html/exam/vendor/topthink/think-swoole/src/Application.php(122): Swoole\Http\Response->write('')
#2 /usr/local/nginx/html/exam/vendor/topthink/think-swoole/src/Http.php(272): think\swoole\Application->swoole(Object(Swoole\Http\Request), Object(Swoole\Http\
Response))
#3 {main}
thrown

将启动命令加上端口号：php think swoole:server -p 9501