TypeError: Argument 1 passed to Drupal\digest\Entity\Digest::send() must implement interface Drupal\user\UserInterface, null given

Error in the logs is:

TypeError: Argument 1 passed to Drupal\digest\Entity\Digest::send() must implement interface Drupal\user\UserInterface, null given, called in /public_html/modules/digest/src/Plugin/QueueWorker/DigestSendQueue.php on line 73 in Drupal\digest\Entity\Digest->send() (line 298 of /public_html/modules/digest/src/Entity/Digest.php)

We suspect this is because a user is deleted after a queue is created, if so, do we need to check that $user != NULL in the processItem method?