Issue #3351772 by T.Barker, gordon, amjad1233, larowlan: php warnings thrown...

Issue #3351772 by T.Barker, gordon, amjad1233, larowlan: php warnings thrown by ClassyLayout when definition_default is NULL for default_section

src/ClassyLayout.php

@@ -20,7 +20,7 @@ class ClassyLayout extends LayoutDefault implements PluginFormInterface {
     $build['#attributes']['class'] = $build['#attributes']['class'] ?? [];
     $definitions = $this->getPluginDefinition()->get('classes');
     foreach ($classes as $key => $class_set) {
-      $definition = $definitions[$key];
+      $definition = $definitions[$key] ?? NULL;
       if (is_string($class_set) && $class_set) {
         $build['#attributes']['class'][] = $class_set;
       }
@@ -66,7 +66,11 @@ class ClassyLayout extends LayoutDefault implements PluginFormInterface {
       if (empty($class_definition['options']) || !is_array($class_definition['options'])) {
         throw new \Exception('The "options" key is required for layout class definitions.');
       }
-      $definition_default = $class_definition['default'] ?? NULL;
+      if ($class_definition['multiple'])  {
+        $definition_default = $class_definition['default'] ?? [];
+      } else {
+        $definition_default = NULL;
+      }
       $form['classes'][$key] = [
         '#title' => $class_definition['label'] ?? $this->t('Classes'),
         '#type' => 'select',

tests/src/Functional/LayoutSectionClassesTest.php

@@ -2,6 +2,8 @@
 
 namespace Drupal\Tests\layout_section_classes\Functional;
 
+use Drupal\Core\Form\FormState;
+use Drupal\layout_builder\LayoutEntityHelperTrait;
 use Drupal\layout_builder\Plugin\SectionStorage\OverridesSectionStorage;
 use Drupal\layout_builder\Section;
 use Drupal\layout_section_classes_test\NewTestClassyLayout;
@@ -15,6 +17,8 @@ use Symfony\Component\DomCrawler\Crawler;
  */
 class LayoutSectionClassesTest extends LayoutBuilderCompatibilityTestBase {
 
+  use LayoutEntityHelperTrait;
+
   /**
    * {@inheritdoc}
    */
@@ -54,6 +58,12 @@ class LayoutSectionClassesTest extends LayoutBuilderCompatibilityTestBase {
     $this->assertCount(1, $crawler->filter('.some-region-classes.a-region-class'));
     // Assert attributes work as expected.
     $this->assertCount(1, $crawler->filter('.background--wave-dark.background--primary-light[data-some-attribute="foo"]'));
+
+    // Check if the default value is an array.
+    $plugin = \Drupal::service('plugin.manager.core.layout')->createInstance('test_layout');
+    $form = $plugin->buildConfigurationForm([], new FormState(), $sections->get(0));
+    $this->assertNotEmpty($form);
+    $this->assertIsArray($form['classes']['style']['#default_value']);
   }
 
   /**