diff -u b/core/modules/comment/src/Plugin/migrate/destination/EntityComment.php b/core/modules/comment/src/Plugin/migrate/destination/EntityComment.php
--- b/core/modules/comment/src/Plugin/migrate/destination/EntityComment.php
+++ b/core/modules/comment/src/Plugin/migrate/destination/EntityComment.php
@@ -109,30 +109,14 @@
   /**
    * {@inheritdoc}
    */
-  protected function getEntity(Row $row, array $old_destination_id_values) {
-    if ($row->isStub()) {
-      $this->processStubRow($row);
-    }
-
-    return parent::getEntity($row, $old_destination_id_values);
-  }
-
-  /**
-   * Specific processing for stub rows.
-   *
-   * @param \Drupal\migrate\Row $row
-   *   The row object.
-   *
-   * @throws \Drupal\migrate\MigrateSkipRowException
-   */
   protected function processStubRow(Row $row) {
+    parent::processStubRow($row);
     $stub_commented_entity_type = $row->getDestinationProperty('entity_type');
 
     // While parent::getEntity() fills the bundle property for stub entities
     // if it's still empty, here we must also make sure entity_id/entity_type
     // are filled (so $comment->getCommentedEntity() always returns a value).
     if (empty($this->stubCommentedEntityIds[$stub_commented_entity_type])) {
-
       // Fill stub entity id. Any id will do, as long as it exists.
       $entity_type = $this->entityManager->getDefinition($stub_commented_entity_type);
       if ($id_key = $entity_type->getKey('id')) {
@@ -142,15 +126,18 @@
           ->execute();
         if ($result) {
           $this->stubCommentedEntityIds[$stub_commented_entity_type] = array_pop($result);
+          $row->setSourceProperty($id_key, $this->stubCommentedEntityIds[$stub_commented_entity_type]);
         }
       }
     }
     if (empty($this->stubCommentedEntityIds[$stub_commented_entity_type])) {
-      throw new MigrateException(t('Could not derive commented entity for comment %id', array('%id' => implode(':', $row->getSourceIdValues()))), MigrationInterface::MESSAGE_ERROR);
+      throw new MigrateException(t('Could not derive commented entity for comment %id', ['%id' => implode(':', $row->getSourceIdValues())]), MigrationInterface::MESSAGE_ERROR);
     }
 
     $row->setDestinationProperty('entity_id', $this->stubCommentedEntityIds[$stub_commented_entity_type]);
     $row->setDestinationProperty('entity_type', $stub_commented_entity_type);
+    $row->setDestinationProperty('created', REQUEST_TIME);
+    $row->setDestinationProperty('changed', REQUEST_TIME);
   }
 
 }
diff -u b/core/modules/comment/src/Tests/Migrate/d6/MigrateCommentTest.php b/core/modules/comment/src/Tests/Migrate/d6/MigrateCommentTest.php
--- b/core/modules/comment/src/Tests/Migrate/d6/MigrateCommentTest.php
+++ b/core/modules/comment/src/Tests/Migrate/d6/MigrateCommentTest.php
@@ -33,8 +33,12 @@
     $this->installEntitySchema('node');
     $this->installEntitySchema('comment');
     $this->installSchema('comment', ['comment_entity_statistics']);
+    $this->installSchema('system', ['router']);
     $this->installConfig(['node', 'comment']);
 
+    // The entity.node.canonical route must exist when the RDF hook is called.
+    $this->container->get('router.builder')->rebuild();
+
     entity_create('node_type', array('type' => 'page'))->save();
     entity_create('node_type', array('type' => 'story'))->save();
     $this->addDefaultCommentField('node', 'story');
reverted:
--- b/core/modules/migrate/src/Plugin/migrate/process/Migration.php
+++ a/core/modules/migrate/src/Plugin/migrate/process/Migration.php
@@ -122,14 +122,6 @@
         $values[$source_id] = $source_id_values[$migration->id()][$index];
       }
 
-      // If we have constants in the source then add them to the values and the
-      // process array.
-      if (isset($migration->get('source')['constants'])) {
-        $constants = $migration->get('source')['constants'];
-        $values += $constants;
-        $process += array_combine(array_keys($constants), array_keys($constants));
-      }
-
       $stub_row = new Row($values + $migration->get('source'), $source_ids, TRUE);
 
       // Do a normal migration with the stub row.
only in patch2:
unchanged:
--- a/core/modules/migrate/src/Plugin/migrate/destination/Entity.php
+++ b/core/modules/migrate/src/Plugin/migrate/destination/Entity.php
@@ -113,12 +113,11 @@ protected function getEntity(Row $row, array $old_destination_id_values) {
       $this->updateEntity($entity, $row);
     }
     else {
-      $values = $row->getDestination();
-      // Stubs might not have the bundle specified.
+      // Stubs might need some required fields filled in.
       if ($row->isStub()) {
-        $values = $this->processStubValues($values);
+        $this->processStubRow($row);
       }
-      $entity = $this->storage->create($values);
+      $entity = $this->storage->create($row->getDestination());
       $entity->enforceIsNew();
     }
     return $entity;
@@ -139,21 +138,14 @@ protected function getEntityId(Row $row) {
   /**
    * Process the stub values.
    *
-   * @param array $values
-   *   An array of destination values.
-   *
-   * @return array
-   *   The processed stub values.
+   * @param \Drupal\migrate\Row $row
+   *   The row of data.
    */
-  protected function processStubValues(array $values) {
-    $values = array_intersect_key($values, $this->getIds());
-
+  protected function processStubRow(Row $row) {
     $bundle_key = $this->getKey('bundle');
-    if ($bundle_key && !isset($values[$bundle_key])) {
-      $values[$bundle_key] = reset($this->bundles);
+    if ($bundle_key && empty($row->getDestinationProperty($bundle_key))) {
+      $row->setDestinationProperty($bundle_key, reset($this->bundles));
     }
-
-    return $values;
   }
 
   /**