Error with latest dev 2.0 - The website encountered an unexpected error. Please try again later.

Problem/Motivation

Drupal 9.2.1
PHP 7.4.0

PHP fatal error error with the latest dev release when clicking "Save settings" for a user:

Error: Call to a member function delete() on null in SITE\web\modules\contrib\notify\src\Form\UserSettings.php on line 231 #0 [internal function]: Drupal\notify\Form\UserSettings->submitForm(Array, Object(Drupal\Core\Form\FormState))

Rolling back to the previous dev snapshot (without the user table formatting) works OK.
I had to uninstall notify, reinstall the older version and replace the tables from backup.

Just to make sure, I got it working again and tried updating again.
Fresh install of latest dev snapshot. Clean (empty) tables notify and notify_submissions

Same problem, fatal error as above when trying to save a user's settings.

Thanks

Steps to reproduce

Install latest dev and run drush updatedb

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes