Error when adding workflow element to webform

Problem/Motivation

After creating a workflow and trying to add it to a webform I get the following error at the top of the "Add Webform workflows element element" pane:

Unable to render elements, please view the below message(s) and the error log.
Drupal\webform_event_dispatcher\Event\WebformElement\WebformElementAlterEvent::getElementType(): Return value must be of type string, null returned
There has been error validating the elements. You may need to edit the YAML source to resolve the issue.

Steps to reproduce

Follow instructions to install module, create workflow and add workflow to a webform.

Thank you!