WSOD after upgrading from 2.0.0-alpha2 to 2.0.0-alpha3: Drupal\site_settings\Plugin\SiteSettingsLoader\FlattenedSiteSettingsLoader::groupKey(): Argument #1 ($group) must be of type string, null given

Problem/Motivation

The upgrade hook 10006 from 2.0.0-alpha2 to 2.0.0-alpha3 probably fails to convert fieldset string to group with machine name.

Steps to reproduce

Tested on Drupal 10.2.2 (before composer update run below)

1. Take a backup of your database!
2. using site_settings 2.0.0-alpha2
3. having 2 Site Setting types setup and site setting entities added
4. composer update, which upgrades site_settings (2.0.0-alpha2 => 2.0.0-alpha3)
5. drush cr
6. Run update hooks drush updb
   Log:

    --------------- --------------------- --------------- ------------------------------------------------------------------------
     Module          Update ID             Type            Description
    --------------- --------------------- --------------- ------------------------------------------------------------------------
     site_settings   10006                 hook_update_n   10006 - Convert fieldset string to group with machine name.
     site_settings   10007                 hook_update_n   10007 - Re-install view.
     site_settings   1_make_revisionable   post-update     Makes site_settings entities revisionable.
     site_settings   2_make_revisionable   post-update     Add default revision values.
     site_settings   check_loader          post-update     Re-run set the default site settings loader to flattened if upgrading.
    --------------- --------------------- --------------- ------------------------------------------------------------------------
    Do you wish to run the specified pending updates? (yes/no) [yes]:
    > yes
   
   >  [notice] Update started: site_settings_update_10006
   >  [notice] Update completed: site_settings_update_10006
   >  [notice] Update started: site_settings_update_10007
   >  [notice] Update completed: site_settings_update_10007
   >  [notice] Update started: site_settings_post_update_1_make_revisionable
   >  [warning] Undefined array key "fieldset" site_settings.post_update.php:64
   >  [notice] Site setting entities have been converted to be revisionable.
   >  [notice] Update completed: site_settings_post_update_1_make_revisionable
   >  [notice] Update started: site_settings_post_update_2_make_revisionable
   >  [notice] Update completed: site_settings_post_update_2_make_revisionable
   >  [notice] Update started: site_settings_post_update_check_loader
   >  [notice] Update completed: site_settings_post_update_check_loader
   

7. Go back to the site to observe the WSOD, error:
   

   The website encountered an unexpected error. Try again later.
   
   TypeError: Drupal\site_settings\Plugin\SiteSettingsLoader\FlattenedSiteSettingsLoader::groupKey(): Argument #1 ($group) must be of type string, null given, called in /var/www/html/web/modules/contrib/site_settings/src/Plugin/SiteSettingsLoader/FlattenedSiteSettingsLoader.php on line 226 in Drupal\site_settings\Plugin\SiteSettingsLoader\FlattenedSiteSettingsLoader->groupKey() (line 394 of modules/contrib/site_settings/src/Plugin/SiteSettingsLoader/FlattenedSiteSettingsLoader.php).
   Drupal\site_settings\Plugin\SiteSettingsLoader\FlattenedSiteSettingsLoader->buildSettings('en') (Line: 167)
   Drupal\site_settings\Plugin\SiteSettingsLoader\FlattenedSiteSettingsLoader->rebuildCache('en') (Line: 158)
   Drupal\site_settings\Plugin\SiteSettingsLoader\FlattenedSiteSettingsLoader->loadAll() (Line: 27)
   site_settings_token_info()
   call_user_func_array(Object, Array) (Line: 409)
   Drupal\Core\Extension\ModuleHandler->Drupal\Core\Extension\{closure}(Object, 'site_settings') (Line: 388)
   Drupal\Core\Extension\ModuleHandler->invokeAllWith('token_info', Object) (Line: 408)
   Drupal\Core\Extension\ModuleHandler->invokeAll('token_info') (Line: 40)
   Drupal\token\Token->getInfo() (Line: 99)
   Drupal\token\Token->getTokenInfo('node', 'path') (Line: 57)
   Drupal\token\TokenModuleProvider->resolveCacheMiss('node::path') (Line: 149)
   Drupal\Core\Cache\CacheCollector->get('node::path') (Line: 49)
   Drupal\token\TokenModuleProvider->getTokenModule('node', 'path') (Line: 1754)
   _field_tokens('entity', Array, Array, Array, Object) (Line: 503)
   token_tokens('entity', Array, Array, Array, Object)
   call_user_func_array(Object, Array) (Line: 409)
   Drupal\Core\Extension\ModuleHandler->Drupal\Core\Extension\{closure}(Object, 'token') (Line: 388)
   Drupal\Core\Extension\ModuleHandler->invokeAllWith('tokens', Object) (Line: 408)
   Drupal\Core\Extension\ModuleHandler->invokeAll('tokens', Array) (Line: 364)
   Drupal\Core\Utility\Token->generate('entity', Array, Array, Array, Object) (Line: 1097)
   token_tokens('node', Array, Array, Array, Object)
   call_user_func_array(Object, Array) (Line: 409)
   Drupal\Core\Extension\ModuleHandler->Drupal\Core\Extension\{closure}(Object, 'token') (Line: 388)
   Drupal\Core\Extension\ModuleHandler->invokeAllWith('tokens', Object) (Line: 408)
   Drupal\Core\Extension\ModuleHandler->invokeAll('tokens', Array) (Line: 364)
   Drupal\Core\Utility\Token->generate('node', Array, Array, Array, Object) (Line: 241)
   Drupal\Core\Utility\Token->doReplace(1, '[node:path]', Array, Array, Object) (Line: 191)
   Drupal\Core\Utility\Token->replace('[node:path]', Array, Array, NULL) (Line: 66)
   Drupal\metatag\MetatagToken->replace('[node:path]', Array, Array) (Line: 789)
   Drupal\metatag\MetatagManager->processTagValue(Object, Array, Array, , 'en') (Line: 628)
   Drupal\metatag\MetatagManager->generateRawElements(Array, Object) (Line: 564)
   Drupal\metatag\MetatagManager->generateElements(Array, Object) (Line: 504)
   metatag_get_tags_from_route() (Line: 258)
   _metatag_remove_duplicate_entity_tags(Array) (Line: 218)
   metatag_entity_view_alter(Array, Object, Object) (Line: 545)
   Drupal\Core\Extension\ModuleHandler->alter('node_view', Array, Object, Object) (Line: 304)
   Drupal\Core\Entity\EntityViewBuilder->buildMultiple(Array) (Line: 238)
   Drupal\Core\Entity\EntityViewBuilder->build(Array)
   call_user_func_array(Array, Array) (Line: 111)
   Drupal\Core\Render\Renderer->doTrustedCallback(Array, Array, 'Render #pre_render callbacks must be methods of a class that implements \Drupal\Core\Security\TrustedCallbackInterface or be an anonymous function. The callback was %s. See https://www.drupal.org/node/2966725', 'exception', 'Drupal\Core\Render\Element\RenderCallbackInterface') (Line: 858)
   Drupal\Core\Render\Renderer->doCallback('#pre_render', Array, Array) (Line: 421)
   Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 240)
   Drupal\Core\Render\Renderer->render(Array, ) (Line: 238)
   Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}() (Line: 627)
   Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 231)
   Drupal\Core\Render\MainContent\HtmlRenderer->prepare(Array, Object, Object) (Line: 128)
   Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object, Object) (Line: 90)
   Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object, 'kernel.view', Object)
   call_user_func(Array, Object, 'kernel.view', Object) (Line: 111)
   Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object, 'kernel.view') (Line: 186)
   Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 76)
   Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 44)
   Drupal\redirect_after_login\RedirectMiddleware->handle(Object, 1, 1) (Line: 58)
   Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
   Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 28)
   Drupal\Core\StackMiddleware\ContentLength->handle(Object, 1, 1) (Line: 32)
   Drupal\big_pipe\StackMiddleware\ContentLength->handle(Object, 1, 1) (Line: 106)
   Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
   Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 48)
   Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 51)
   Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 36)
   Drupal\Core\StackMiddleware\AjaxPageState->handle(Object, 1, 1) (Line: 51)
   Drupal\Core\StackMiddleware\StackedHttpKernel->handle(Object, 1, 1) (Line: 704)
   Drupal\Core\DrupalKernel->handle(Object) (Line: 19)
   

Only way to bring the site back is to rollback the composer update and re-import an archive db.

Proposed resolution

I suspect that the upgrade hook is failing doing the conversion of fieldset string to group with machine name.

Remaining tasks

Fix the upgrade hook.