Customize: Removing setting from changeset generates PHP warning

[dlh]

WP_Customize_Manager::save_changeset_post() includes a check for array_key_exists( 'value', $setting_params ) while looping through $args['data'].

This check can generate a warning when removing a setting from the changeset by passing 'setting_id' => null.

The attached patch includes a PHPUnit test demonstrating the issue; it should also be replicable in JS by calling wp.customize.requestChangesetUpdate( { 'setting_id': null } ).

The patch would verify that $setting_params is an array before checking array_key_exists().

[westonruter]

@dlh @stubgo did you encounter this in writing unit tests for the changesets REST API endpoint? If not, could you add a unit test for it there as well to ensure that this use case is tested?

[westonruter]

In 41243:

Customize: Fix PHP warning raised when deleting a setting from changeset via passing null as params in WP_Customize_Manager::save_changeset_post().

Props dlh.
Fixes #41621.

[dlh]

Replying to westonruter:

@dlh @stubgo did you encounter this in writing unit tests for the changesets REST API endpoint? If not, could you add a unit test for it there as well to ensure that this use case is tested?

I encountered it separately from the endpoints, but it looks like @stubgo already wrote a test for it: ​https://github.com/WP-API/wp-api-customize-endpoints/blob/304196b1e65382393c10f883e3e1e050b54bc3a4/tests/test-customize-changesets-controller.php#L1906.