Issue #3335269 by Niklan: Entity stubs doesn't follows fallback logic from entities and leads to a broken migration

core/modules/migrate/src/Plugin/migrate/destination/EntityContentBase.php

@@ -338,9 +338,10 @@ class EntityContentBase extends Entity implements HighestIdInterface, MigrateVal
       $row->setDestinationProperty($bundle_key, reset($this->bundles));
     }
 
+    $bundle = $row->getDestinationProperty($bundle_key) ?? $this->storage->getEntityTypeId();
     // Populate any required fields not already populated.
     $fields = $this->entityFieldManager
-      ->getFieldDefinitions($this->storage->getEntityTypeId(), $row->getDestinationProperty($bundle_key));
+      ->getFieldDefinitions($this->storage->getEntityTypeId(), $bundle);
     foreach ($fields as $field_name => $field_definition) {
       if ($field_definition->isRequired() && is_null($row->getDestinationProperty($field_name))) {
         // Use the configured default value for this specific field, if any.

core/modules/migrate/tests/src/Kernel/MigrateEntityContentBaseTest.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\Tests\migrate\Kernel;
 
+use Drupal\Core\Entity\EntityFieldManager;
 use Drupal\entity_test\Entity\EntityTestMul;
 use Drupal\KernelTests\KernelTestBase;
 use Drupal\language\Entity\ConfigurableLanguage;
@@ -10,6 +11,7 @@ use Drupal\migrate\Plugin\migrate\destination\EntityContentBase;
 use Drupal\migrate\Plugin\MigrateIdMapInterface;
 use Drupal\migrate\Plugin\MigrationInterface;
 use Drupal\migrate\Row;
+use Drupal\migrate_drupal\Tests\StubTestTrait;
 use Drupal\migrate_entity_test\Entity\StringIdEntityTest;
 
 /**
@@ -19,6 +21,8 @@ use Drupal\migrate_entity_test\Entity\StringIdEntityTest;
  */
 class MigrateEntityContentBaseTest extends KernelTestBase {
 
+  use StubTestTrait;
+
   /**
    * Modules to enable.
    *
@@ -304,4 +308,48 @@ class MigrateEntityContentBaseTest extends KernelTestBase {
     }
   }
 
+  /**
+   * Tests bundle is properly provided for stubs without bundle support.
+   *
+   * @todo Remove this test in when native PHP type-hints will be added for
+   *   EntityFieldManagerInterface::getFieldDefinitions(). See
+   *   https://www.drupal.org/project/drupal/issues/3050720.
+   */
+  public function testBundleFallbackForStub(): void {
+    $this->enableModules(['migrate_entity_test']);
+    $this->installEntitySchema('migrate_string_id_entity_test');
+
+    $entity_type_manager = $this->container->get('entity_type.manager');
+    $entity_type_bundle_info = $this->container->get('entity_type.bundle.info');
+    $entity_display_repository = $this
+      ->container
+      ->get('entity_display.repository');
+    $typed_data_manager = $this->container->get('typed_data_manager');
+    $language_manager = $this->container->get('language_manager');
+    $keyvalue = $this->container->get('keyvalue');
+    $module_handler = $this->container->get('module_handler');
+    $cache_discovery = $this->container->get('cache.discovery');
+    $entity_last_installed_schema_repository = $this
+      ->container
+      ->get('entity.last_installed_schema.repository');
+
+    $decorated_entity_field_manager = new class ($entity_type_manager, $entity_type_bundle_info, $entity_display_repository, $typed_data_manager, $language_manager, $keyvalue, $module_handler, $cache_discovery, $entity_last_installed_schema_repository) extends EntityFieldManager {
+
+      /**
+       * {@inheritdoc}
+       */
+      public function getFieldDefinitions($entity_type_id, $bundle) {
+        if (\is_null($bundle)) {
+          throw new \Exception("Bundle value shouldn't be NULL.");
+        }
+
+        return parent::getFieldDefinitions($entity_type_id, $bundle);
+      }
+
+    };
+
+    $this->container->set('entity_field.manager', $decorated_entity_field_manager);
+    $this->createEntityStub('migrate_string_id_entity_test');
+  }
+
 }