提问前请务必仔细阅读 如何排查故障 和 常见问题。
问题描述：
Flarum更新后提示需要php8.1，更换为php8.1后更新，报错
报错内容：
Deprecated: mb_strwidth(): Passing null to parameter #1 ($string) of type string is deprecated in /www/wwwroot/mclive.org/vendor/illuminate/support/Str.php on line 363
Fatal error: Uncaught Laminas\HttpHandlerRunner\Exception\EmitterException: Output has been emitted previously; cannot emit response in /www/wwwroot/mclive.org/vendor/laminas/laminas-httphandlerrunner/src/Exception/EmitterException.php:20 Stack trace: #0 /www/wwwroot/mclive.org/vendor/laminas/laminas-httphandlerrunner/src/Emitter/SapiEmitterTrait.php(42): Laminas\HttpHandlerRunner\Exception\EmitterException::forOutputSent() #1 /www/wwwroot/mclive.org/vendor/laminas/laminas-httphandlerrunner/src/Emitter/SapiEmitter.php(21): Laminas\HttpHandlerRunner\Emitter\SapiEmitter->assertNoPreviousOutput() #2 /www/wwwroot/mclive.org/vendor/laminas/laminas-httphandlerrunner/src/RequestHandlerRunner.php(75): Laminas\HttpHandlerRunner\Emitter\SapiEmitter->emit() #3 /www/wwwroot/mclive.org/vendor/flarum/core/src/Http/Server.php(45): Laminas\HttpHandlerRunner\RequestHandlerRunner->run() #4 /www/wwwroot/mclive.org/public/index.php(26): Flarum\Http\Server->listen() #5 {main} thrown in /www/wwwroot/mclive.org/vendor/laminas/laminas-httphandlerrunner/src/Exception/EmitterException.php on line 20
调试模式报错内容：
已尝试的解决办法：
退回php7.2，无效
网址：mclive.org