Views Modal UI fails

Problem/Motivation

When editing a view and adding a new Simple Math field, the Views modal dialog fails. Existing and populated fields don't cause errors. Not sure when this started,

Steps to reproduce

• Create a view with fields, add a new Simple Math field. The views add field UI does not close or give confirmation that the field was created.
• Closing the modal and/or refreshing the page shows new fields added.
• Clicking to edit the fields throws an Ajax error with views throwing a error message:
  Error message
  Oops, something went wrong. Check your browser's developer console for more details.

A work around: right click the field and open the dialog in a new tab. Then you can edit the field and the error will stop in the main Views UI

On my local, with error reporting turned on, the dialog on the new tab showed:

Warning: Trying to access array offset on value of type null in /var/www/html/web/modules/contrib/views_simple_math_field/src/Plugin/views/field/SimpleMathField.php on line 116

Warning: Trying to access array offset on value of type null in /var/www/html/web/modules/contrib/views_simple_math_field/src/Plugin/views/field/SimpleMathField.php on line 122

Warning: foreach() argument must be of type array|object, null given in /var/www/html/web/core/lib/Drupal/Core/Render/Element/Checkboxes.php on line 113