Custom Field error triggered campaing

Your software
My Mautic version is: 3.3.1
My PHP version is: 7.3.27
My Database type and version is: MySql docker container

Your problem
My problem is:
I created a custom field of type select so I filled it in with three values … after I created a new campaign with a conditional verifying this custom field … when the campaign was launched I received this message in the mautic log.

screenshot 1 - conditional screen

screenshot 2 - custom field detail

These errors are showing in the log:
[2021-05-19 10:02:02] mautic.NOTICE: Symfony\Component\Debug\Exception\FatalThrowableError: Type error: Argument 1 passed to Mautic\LeadBundle\Helper\CustomFieldHelper::fieldValueTransfomer() must be of the type array, null given, called in /var/www/html/app/bundles/LeadBundle/EventListener/CampaignSubscriber.php on line 502 (uncaught exception) at /var/www/html/app/bundles/LeadBundle/Helper/CustomFieldHelper.php line 60 while running console command mautic:campaigns:trigger
[2021-05-19 10:02:02] mautic.WARNING: Command mautic:campaigns:trigger exited with status code 1

Steps I have tried to fix the problem: