Cannot split from a post with deleted user

[clarkwinkelmann]

Bug Report

Current Behavior
If you start the split from a post with [deleted] user, the split fails with a 500 error.

Steps to Reproduce

1. Create discussion with 2+ posts
2. Delete author of second post, or use Author Change extension to manually remove the author
3. Split from second post
4. See "Oops something went wrong" red error message

Error message from log file:

[2021-06-02 23:13:04] flarum.ERROR: TypeError: Argument 2 passed to Flarum\Discussion\Discussion::start() must be an instance of Flarum\User\User, null given, called in /home/clark/Projects/flarum-1.0/vendor/fof/split/src/Api/Commands/SplitDiscussionHandler.php on line 97 and defined in /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Discussion/Discussion.php:120
Stack trace:
#0 /home/clark/Projects/flarum-1.0/vendor/fof/split/src/Api/Commands/SplitDiscussionHandler.php(97): Flarum\Discussion\Discussion::start()
#1 /home/clark/Projects/flarum-1.0/vendor/illuminate/bus/Dispatcher.php(122): FoF\Split\Api\Commands\SplitDiscussionHandler->handle()
#2 /home/clark/Projects/flarum-1.0/vendor/illuminate/pipeline/Pipeline.php(128): Illuminate\Bus\Dispatcher->Illuminate\Bus\{closure}()
#3 /home/clark/Projects/flarum-1.0/vendor/illuminate/pipeline/Pipeline.php(103): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}()
#4 /home/clark/Projects/flarum-1.0/vendor/illuminate/bus/Dispatcher.php(132): Illuminate\Pipeline\Pipeline->then()
#5 /home/clark/Projects/flarum-1.0/vendor/illuminate/bus/Dispatcher.php(78): Illuminate\Bus\Dispatcher->dispatchNow()
#6 /home/clark/Projects/flarum-1.0/vendor/fof/split/src/Api/Controllers/SplitController.php(61): Illuminate\Bus\Dispatcher->dispatch()
#7 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Api/Controller/AbstractSerializeController.php(110): FoF\Split\Api\Controllers\SplitController->data()
#8 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Http/RouteHandlerFactory.php(41): Flarum\Api\Controller\AbstractSerializeController->handle()
#9 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Http/Middleware/ExecuteRoute.php(27): Flarum\Http\RouteHandlerFactory->Flarum\Http\{closure}()
#10 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Flarum\Http\Middleware\ExecuteRoute->process()
#11 /home/clark/Projects/flarum-1.0/workbench/flarum-ext-audit/src/Middlewares/ExtendSetPermissionController.php(19): Laminas\Stratigility\Next->handle()
#12 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Kilowhat\Audit\Middlewares\ExtendSetPermissionController->process()
#13 /home/clark/Projects/flarum-1.0/workbench/flarum-ext-audit/src/Middlewares/SetLoggerActor.php(28): Laminas\Stratigility\Next->handle()
#14 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Kilowhat\Audit\Middlewares\SetLoggerActor->process()
#15 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Api/Middleware/ThrottleApi.php(33): Laminas\Stratigility\Next->handle()
#16 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Flarum\Api\Middleware\ThrottleApi->process()
#17 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Http/Middleware/CheckCsrfToken.php(44): Laminas\Stratigility\Next->handle()
#18 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Flarum\Http\Middleware\CheckCsrfToken->process()
#19 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Http/Middleware/ResolveRoute.php(67): Laminas\Stratigility\Next->handle()
#20 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Flarum\Http\Middleware\ResolveRoute->process()
#21 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Http/Middleware/SetLocale.php(51): Laminas\Stratigility\Next->handle()
#22 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Flarum\Http\Middleware\SetLocale->process()
#23 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Http/Middleware/AuthenticateWithHeader.php(56): Laminas\Stratigility\Next->handle()
#24 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Flarum\Http\Middleware\AuthenticateWithHeader->process()
#25 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Http/Middleware/AuthenticateWithSession.php(31): Laminas\Stratigility\Next->handle()
#26 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Flarum\Http\Middleware\AuthenticateWithSession->process()
#27 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Http/Middleware/RememberFromCookie.php(52): Laminas\Stratigility\Next->handle()
#28 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Flarum\Http\Middleware\RememberFromCookie->process()
#29 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Http/Middleware/StartSession.php(61): Laminas\Stratigility\Next->handle()
#30 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Flarum\Http\Middleware\StartSession->process()
#31 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Api/Middleware/FakeHttpMethods.php(29): Laminas\Stratigility\Next->handle()
#32 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Flarum\Api\Middleware\FakeHttpMethods->process()
#33 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Http/Middleware/ParseJsonBody.php(28): Laminas\Stratigility\Next->handle()
#34 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Flarum\Http\Middleware\ParseJsonBody->process()
#35 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Http/Middleware/HandleErrors.php(57): Laminas\Stratigility\Next->handle()
#36 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Flarum\Http\Middleware\HandleErrors->process()
#37 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Http/Middleware/InjectActorReference.php(25): Laminas\Stratigility\Next->handle()
#38 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Flarum\Http\Middleware\InjectActorReference->process()
#39 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/MiddlewarePipe.php(84): Laminas\Stratigility\Next->handle()
#40 /home/clark/Projects/flarum-1.0/vendor/middlewares/request-handler/src/RequestHandler.php(84): Laminas\Stratigility\MiddlewarePipe->process()
#41 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Middlewares\RequestHandler->process()
#42 /home/clark/Projects/flarum-1.0/vendor/middlewares/base-path-router/src/BasePathRouter.php(101): Laminas\Stratigility\Next->handle()
#43 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Middlewares\BasePathRouter->process()
#44 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Middleware/OriginalMessages.php(42): Laminas\Stratigility\Next->handle()
#45 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Laminas\Stratigility\Middleware\OriginalMessages->process()
#46 /home/clark/Projects/flarum-1.0/vendor/middlewares/base-path/src/BasePath.php(73): Laminas\Stratigility\Next->handle()
#47 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Middlewares\BasePath->process()
#48 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Http/Middleware/ProcessIp.php(24): Laminas\Stratigility\Next->handle()
#49 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/Next.php(61): Flarum\Http\Middleware\ProcessIp->process()
#50 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/MiddlewarePipe.php(84): Laminas\Stratigility\Next->handle()
#51 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-stratigility/src/MiddlewarePipe.php(73): Laminas\Stratigility\MiddlewarePipe->process()
#52 /home/clark/Projects/flarum-1.0/vendor/laminas/laminas-httphandlerrunner/src/RequestHandlerRunner.php(96): Laminas\Stratigility\MiddlewarePipe->handle()
#53 /home/clark/Projects/flarum-1.0/vendor/flarum/core/src/Http/Server.php(44): Laminas\HttpHandlerRunner\RequestHandlerRunner->run()
#54 /home/clark/Projects/flarum-1.0/public/index.php(26): Flarum\Http\Server->listen()
#55 {main}  

Screenshots
(modal backdrop altered to better show what's behind it)

Environment

• Flarum version: 1.0.1
• Extension version: 1.0.0

Possible solution(s)
The problem is that Flarum's Discussion::start() method does not accept null as the author. I don't think there's an issue for it at the Flarum level yet.

A workaround would be to create the discussion model without using Discussion::start.