diff --git a/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/field_type/ConfigurableEntityReferenceItem.php b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/field_type/ConfigurableEntityReferenceItem.php
index bf4bbb4..299780a 100644
--- a/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/field_type/ConfigurableEntityReferenceItem.php
+++ b/core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/field/field_type/ConfigurableEntityReferenceItem.php
@@ -70,7 +70,7 @@ public function preSave() {
     $entity = $this->get('entity')->getValue();
     $target_id = $this->get('target_id')->getValue();
 
-    if (empty($target_id) && !empty($entity) && $entity->isNew()) {
+    if ($target_id === NULL && !empty($entity) && $entity->isNew()) {
       $entity->save();
       $this->set('target_id', $entity->id());
     }
diff --git a/core/modules/field/field.module b/core/modules/field/field.module
index c3e056d..92f8819 100644
--- a/core/modules/field/field.module
+++ b/core/modules/field/field.module
@@ -127,17 +127,21 @@ function field_help($path, $arg) {
       $field_widgets = \Drupal::service('plugin.manager.field.widget')->getDefinitions();
       $field_types = \Drupal::service('plugin.manager.entity.field.field_type')->getDefinitions();
       foreach (array_merge($field_types, $field_widgets) as $field_module) {
-        $modules[] = $field_module['provider'];
+        $providers[] = $field_module['provider'];
       }
-      $modules = array_unique($modules);
-      sort($modules);
-      foreach ($modules as $module) {
-        $display = $info[$module]['name'];
-        if (\Drupal::moduleHandler()->implementsHook($module, 'help')) {
-          $items[] = l($display, 'admin/help/' . $module);
-        }
-        else {
-          $items[] = $display;
+      $providers = array_unique($providers);
+      sort($providers);
+      foreach ($providers as $provider) {
+        // @todo: Throws notices because the owner of field types in
+        //   \Drupal\Core\Entity is 'Core'.
+        if (isset($info[$provider]['name'])) {
+          $display = $info[$provider]['name'];
+          if (\Drupal::moduleHandler()->implementsHook($provider, 'help')) {
+            $items[] = l($display, 'admin/help/' . $provider);
+          }
+          else {
+            $items[] = $display;
+          }
         }
       }
       $item_list = array(
diff --git a/core/modules/user/lib/Drupal/user/Entity/User.php b/core/modules/user/lib/Drupal/user/Entity/User.php
index d8dc8e4..693751e 100644
--- a/core/modules/user/lib/Drupal/user/Entity/User.php
+++ b/core/modules/user/lib/Drupal/user/Entity/User.php
@@ -58,6 +58,14 @@ public function id() {
   /**
    * {@inheritdoc}
    */
+  public function isNew() {
+    // ID 0 does not imply a new user.
+    return !empty($this->enforceIsNew) || $this->id() === NULL;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   static function preCreate(EntityStorageControllerInterface $storage_controller, array &$values) {
     parent::preCreate($storage_controller, $values);