Cannot add MerlinOne Search widget to Entity Browser

Problem/Motivation

Cannot get this module to work with the entity browser.

Steps to reproduce

Go to admin/config/content/entity_browser/%entity_browser_name%/widgets
In the 'Add widget plugin' select list, select MerlinOne Search
Get an ajax error, and the widget will not be added. Note the error in the dblog:

AssertionError: Cannot load the "media_type" entity with NULL ID. in assert() (line 261 of /var/www/html/web/core/lib/Drupal/Core/Entity/EntityStorageBase.php).

I have tested this on a 9.5.9 site and a completely bare install of 10.1.1 (with changes to enable it to install on D10)