Issue #3190261 by danflanagan8, doostinharrell, phenaproxima, larowlan,...

Issue #3190261 by danflanagan8, doostinharrell, phenaproxima, larowlan, paulocs: MediaLibraryWidget can trigger an AJAX error if all media types can be referenced

(cherry picked from commit 458aa2cb)

core/modules/media_library/src/Plugin/Field/FieldWidget/MediaLibraryWidget.php

@@ -305,7 +305,8 @@ public function formElement(FieldItemListInterface $items, $delta, array $elemen
     $element += [
       '#type' => 'fieldset',
       '#cardinality' => $this->fieldDefinition->getFieldStorageDefinition()->getCardinality(),
-      '#target_bundles' => $settings['target_bundles'] ?? FALSE,
+      // If no target bundles are specified, all target bundles are allowed.
+      '#target_bundles' => $settings['target_bundles'] ?? [],
       '#attributes' => [
         'id' => $wrapper_id,
         'class' => ['js-media-library-widget'],

core/modules/media_library/tests/src/FunctionalJavascript/EntityReferenceWidgetTest.php

@@ -140,7 +140,12 @@ public function testWidget() {
     $this->assertTrue($menu->hasLink('Type Three'));
     $this->assertTrue($menu->hasLink('Type Four'));
     $this->assertTrue($menu->hasLink('Type Five'));
-    $assert_session->elementExists('css', '.ui-dialog-titlebar-close')->click();
+
+    // Insert media to test validation with null target_bundles.
+    $this->switchToMediaType('One');
+    $this->assertNotEmpty($assert_session->waitForText('Showing Type One media.'));
+    $this->selectMediaItem(0);
+    $this->pressInsertSelected('Added one media item.');
 
     // Assert that the media type menu is not available when only 1 type is
     // configured for the field.