Undefined array key comment_notify when a user has only entity_notify saved

Problem/Motivation

When Comment Notify loads the comment form, it retrieves the current user’s comment_notify preference.

The module assumes that a user with stored Comment Notify settings has both entity_notify and comment_notify values. However, users can have only entity_notify stored. In that case, UserNotificationSettings::getSetting() attempts to access a missing array key and PHP emits:

Warning: Undefined array key "comment_notify" in src/UserNotificationSettings.php

This was observed while users reviewed unpublished Article content with an enabled comment field.

Steps to reproduce

1. Install Comment Notify 8.x-1.5.
2. Enable Comment Notify for an entity bundle with a comment field.
3. Create a user with permission to subscribe to comments.
4. Store only an entity_notify preference for that user, without storing comment_notify.
5. Visit content where the enabled comment form is displayed as that user.

For example, the incomplete preference state can be created with:

$user_settings->saveSettings($uid, COMMENT_NOTIFY_ENTITY);

Proposed resolution

When a stored settings array does not contain the requested preference, merge the configured default settings before returning the requested value.

This preserves explicitly stored preferences and uses the configured default only for the missing key.

The attached patch:

• Updates src/UserNotificationSettings.php to apply defaults for an individual missing preference.
• Adds a functional regression test for a user with only entity_notify stored.

Remaining tasks

• Review and test the attached patch.

User interface changes

None.

API changes

None.

Data model changes

None.