Undefined array key "base64_encoded" when editing key form

Problem/Motivation

After a key is correctly set in the remote site, when revisiting the edit page an error is reported about missing array key for "base64_encoded".

Error message
Warning: Undefined array key "base64_encoded" in Drupal\pantheon_secrets\Plugin\KeyProvider\PantheonSecretKeyProvider->buildConfigurationForm() (line 81 of modules/contrib/pantheon_secrets/src/Plugin/KeyProvider/PantheonSecretKeyProvider.php).

Installed module version from composer.lock:

"name": "drupal/pantheon_secrets",
            "version": "1.0.5",

Steps to reproduce

Edit an existing key that was set to Pantheon Key Provider. So far, we only have confirmed the bug when the checkbox for "base64_encoded" is unchecked.

Proposed resolution

I don't see the "base64_encoded" key in the exported key config. Is it missing from schema? When it is false, is it not getting set into the config?

Thank you for looking into this! Awesome module btw! Thanks for the early access!