8.x-1.0-beta5 release?

https://www.drupal.org/project/workbench_access/issues/3231757#comment-14211411

https://git.drupalcode.org/project/workbench_access/-/blob/8.x-1.x/src/Plugin/EntityReferenceSelection/TaxonomyHierarchySelection.php
The fixes isset was released a while ago on 8.x-1.0-dev  but for those moving into drupal9 this is an issue with the current beta4 release.