User with local ID 0 does not have a global account.
from /srv/mediawiki/php-1.46.0-wmf.17/extensions/CampaignEvents/src/MWEntity/CampaignsCentralUserLookup.php(48)
#0 /srv/mediawiki/php-1.46.0-wmf.17/extensions/CampaignEvents/src/EventContribution/EventContributionValidator.php(127): MediaWiki\Extension\CampaignEvents\MWEntity\CampaignsCentralUserLookup->newFromUserIdentity(MediaWiki\User\UserIdentityValue)
#1 /srv/mediawiki/php-1.46.0-wmf.17/extensions/CampaignEvents/src/Rest/EventContributionsHandler.php(37): MediaWiki\Extension\CampaignEvents\EventContribution\EventContributionValidator->validateAndSchedule(MediaWiki\Extension\CampaignEvents\Event\ExistingEventRegistration, int, string, MediaWiki\User\User)
#2 /srv/mediawiki/php-1.46.0-wmf.17/includes/Rest/SimpleHandler.php(41): MediaWiki\Extension\CampaignEvents\Rest\EventContributionsHandler->run(int, string, string)
#3 /srv/mediawiki/php-1.46.0-wmf.17/includes/Rest/Module/Module.php(472): MediaWiki\Rest\SimpleHandler->execute()
#4 /srv/mediawiki/php-1.46.0-wmf.17/includes/Rest/Module/Module.php(301): MediaWiki\Rest\Module\Module->executeHandler(MediaWiki\Extension\CampaignEvents\Rest\EventContributionsHandler)
#5 /srv/mediawiki/php-1.46.0-wmf.17/includes/Rest/Router.php(484): MediaWiki\Rest\Module\Module->execute(string, MediaWiki\Rest\RequestFromGlobals)
#6 /srv/mediawiki/php-1.46.0-wmf.17/includes/Rest/Router.php(443): MediaWiki\Rest\Router->doExecute(string, MediaWiki\Rest\RequestFromGlobals)
#7 /srv/mediawiki/php-1.46.0-wmf.17/includes/Rest/EntryPoint.php(181): MediaWiki\Rest\Router->execute(MediaWiki\Rest\RequestFromGlobals)
#8 /srv/mediawiki/php-1.46.0-wmf.17/includes/MediaWikiEntryPoint.php(180): MediaWiki\Rest\EntryPoint->execute()
#9 /srv/mediawiki/php-1.46.0-wmf.17/rest.php(25): MediaWiki\MediaWikiEntryPoint->run()
#10 /srv/mediawiki/w/rest.php(3): require(string)
#11 {main}