Warning: Undefined array key "default_layout"

Problem/Motivation

Multiple PHP warnings get triggered when inserting a new grid block.

Warning: Undefined array key "default_layout" in Drupal\ckeditor_bs_grid\Form\GridDialog->buildLayoutStep() (line 274 of /var/www/html/web/modules/contrib/ckeditor_bs_grid/src/Form/GridDialog.php).

// Allow defaulting by sort order instead.
      elseif ($breakpoint['columns'][$num_cols]['default_layout'] === 'order') {
        $keys = array_keys($options);
        $default_layout = $keys[1] ?? $default_layout;
      }

I don't know what the default behavior should be here, so I can't offer a fix, but I'm attaching a minimal patch to suppress the warning messages - should someone need it.

The warnings are not triggered by editing an existing grid block.

Steps to reproduce

PHP 8.2.15
Drupal core 10.2.5
CKEditor Bootstrap Grid 2.0.11

1. Start creating or editing content.
2. Click on the insert grid icon.
3. Click next.
4. Check the logs for the triggered warnings.

Proposed resolution

Fix the default logic.

Remaining tasks

User interface changes

API changes

Data model changes