Fatal error after update: Return value of Consumer::getClientId() must be string, null returned

Problem/Motivation

When running "composer update" on my drupal 9.4 project, drupal/consumers was updated from 1.13.0 to 1.19.0. Now I get a fatal error:

TypeError: Return value of Drupal\consumers\Entity\Consumer::getClientId() must be of the type string, null returned
 in Drupal\consumers\Entity\Consumer->getClientId()
 (line 271 of modules/contrib/consumers/src/Entity/Consumer.php). 

This was already reported by others in the simple_oauth package 🐛 Consumer list page showing WSOD after upgrade Closed: won't fix , but rejected there.

Proposed resolution

Automatic migration for consumers without client IDs, or cast null client IDs to empty strings.