diff --git a/core/lib/Drupal/Core/Entity/Entity.php b/core/lib/Drupal/Core/Entity/Entity.php
index 94ce03c..28744be 100644
--- a/core/lib/Drupal/Core/Entity/Entity.php
+++ b/core/lib/Drupal/Core/Entity/Entity.php
@@ -72,7 +72,7 @@ public function uuid() {
    * {@inheritdoc}
    */
   public function isNew() {
-    return !empty($this->enforceIsNew) || !$this->id();
+    return !empty($this->enforceIsNew) || $this->id() === NULL;
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Entity/Field/FieldTypePluginManager.php b/core/lib/Drupal/Core/Entity/Field/FieldTypePluginManager.php
index b9168d5..78ba0e1 100644
--- a/core/lib/Drupal/Core/Entity/Field/FieldTypePluginManager.php
+++ b/core/lib/Drupal/Core/Entity/Field/FieldTypePluginManager.php
@@ -66,7 +66,6 @@ public function processDefinition(&$definition, $plugin_id) {
     }
   }
 
-
   /**
    * Returns the default field-level settings for a field type.
    *
@@ -100,21 +99,22 @@ public function getDefaultInstanceSettings($type) {
   /**
    * Gets the definition of all field types.
    *
-   * @param Boolean $configurable
-   *   Configurable flag to indicate whether return configurable field types.
+   * @param bool $configurable
+   *   (optional) Whether to return only configurable field types. Defaults to
+   *   FALSE.
    *
    * @return array
    *   An array of field type definitions.
    */
-  public function getDefinitions($configurable = NULL) {
+  public function getDefinitions($configurable = FALSE) {
     $definitions = $this->getCachedDefinitions();
     if (!isset($definitions)) {
       $definitions = $this->findDefinitions();
       $this->setCachedDefinitions($definitions);
     }
     if ($configurable) {
-      return array_filter($this->definitions, function ($defintion) {
-        return $defintion['configurable'];
+      return array_filter($this->definitions, function ($definition) {
+        return $definition['configurable'];
       });
     }
     return $definitions;
diff --git a/core/modules/comment/lib/Drupal/comment/Plugin/field/field_type/CommentItem.php b/core/modules/comment/lib/Drupal/comment/Plugin/field/field_type/CommentItem.php
index ea8f916..7cefb45 100644
--- a/core/modules/comment/lib/Drupal/comment/Plugin/field/field_type/CommentItem.php
+++ b/core/modules/comment/lib/Drupal/comment/Plugin/field/field_type/CommentItem.php
@@ -51,8 +51,8 @@ public function getPropertyDefinitions() {
           'label' => t('Comment status value'),
         ),
         'cid' => array(
+          'type' => 'integer',
           'label' => t('Last comment ID'),
-          'type' => 'integer',
         ),
         'last_comment_timestamp' => array(
           'label' => t('Last comment timestamp'),
diff --git a/core/modules/entity_reference/entity_reference.module b/core/modules/entity_reference/entity_reference.module
index 5d2632c..6ba7203 100644
--- a/core/modules/entity_reference/entity_reference.module
+++ b/core/modules/entity_reference/entity_reference.module
@@ -15,7 +15,7 @@
  * Implements hook_field_info_alter().
  */
 function entity_reference_field_info_alter(&$info) {
-  // Make he entity reference field configurable.
+  // Make the entity reference field configurable.
   $info['entity_reference']['configurable'] = TRUE;
   $info['entity_reference']['class'] = '\Drupal\entity_reference\Plugin\field\field_type\ConfigurableEntityReferenceItem';
   $info['entity_reference']['list_class'] = '\Drupal\field\Plugin\Type\FieldType\ConfigFieldItemList';
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 299780a..491cd16 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 ($target_id === NULL && !empty($entity) && $entity->isNew()) {
+    if (!$target_id && !empty($entity) && $entity->isNew()) {
       $entity->save();
       $this->set('target_id', $entity->id());
     }
diff --git a/core/modules/field/field.module b/core/modules/field/field.module
index 92f8819..638d3af 100644
--- a/core/modules/field/field.module
+++ b/core/modules/field/field.module
@@ -132,8 +132,8 @@ function field_help($path, $arg) {
       $providers = array_unique($providers);
       sort($providers);
       foreach ($providers as $provider) {
-        // @todo: Throws notices because the owner of field types in
-        //   \Drupal\Core\Entity is 'Core'.
+        // Skip plugins provided by core components as they do not implement
+        // hook_help().
         if (isset($info[$provider]['name'])) {
           $display = $info[$provider]['name'];
           if (\Drupal::moduleHandler()->implementsHook($provider, 'help')) {
diff --git a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldTest.php b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldTest.php
index 30fea9e..79a143d 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldTest.php
@@ -355,8 +355,8 @@ protected function checkIntrospection($entity_type) {
     // @todo: Make this work without having to create entity objects.
     $entity = entity_create($entity_type, array());
     $definitions = $entity->getPropertyDefinitions();
-    $this->assertEqual($definitions['name']['type'], 'string_field', $entity_type .': Name field found.');
-    $this->assertEqual($definitions['user_id']['type'], 'entity_reference_field', $entity_type .': User field found.');
+    $this->assertEqual($definitions['name']['type'], 'field_item:string', $entity_type .': Name field found.');
+    $this->assertEqual($definitions['user_id']['type'], 'field_item:entity_reference', $entity_type .': User field found.');
     $this->assertEqual($definitions['field_test_text']['type'], 'field_item:text', $entity_type .': Test-text-field field found.');
 
     // Test introspecting an entity object.
@@ -364,8 +364,8 @@ protected function checkIntrospection($entity_type) {
     $entity = entity_create($entity_type, array());
 
     $definitions = $entity->getPropertyDefinitions();
-    $this->assertEqual($definitions['name']['type'], 'string_field', $entity_type .': Name field found.');
-    $this->assertEqual($definitions['user_id']['type'], 'entity_reference_field', $entity_type .': User field found.');
+    $this->assertEqual($definitions['name']['type'], 'field_item:string', $entity_type .': Name field found.');
+    $this->assertEqual($definitions['user_id']['type'], 'field_item:entity_reference', $entity_type .': User field found.');
     $this->assertEqual($definitions['field_test_text']['type'], 'field_item:text', $entity_type .': Test-text-field field found.');
 
     $name_properties = $entity->name->getPropertyDefinitions();
diff --git a/core/modules/user/lib/Drupal/user/Entity/User.php b/core/modules/user/lib/Drupal/user/Entity/User.php
index 693751e..d8dc8e4 100644
--- a/core/modules/user/lib/Drupal/user/Entity/User.php
+++ b/core/modules/user/lib/Drupal/user/Entity/User.php
@@ -58,14 +58,6 @@ public function id() {
   /**
    * {@inheritdoc}
    */
-  public function isNew() {
-    // ID 0 does not imply a new user.
-    return !empty($this->enforceIsNew) || $this->id() === NULL;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
   static function preCreate(EntityStorageControllerInterface $storage_controller, array &$values) {
     parent::preCreate($storage_controller, $values);
 
diff --git a/core/modules/user/lib/Drupal/user/Tests/UserValidationTest.php b/core/modules/user/lib/Drupal/user/Tests/UserValidationTest.php
index 99aaecb..46037f8 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserValidationTest.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserValidationTest.php
@@ -108,10 +108,12 @@ function testValidation() {
 
     $mail = $this->randomName(EMAIL_MAX_LENGTH - 11) . '@example.com';
     $user->set('mail', $mail);
+    // @todo: There are two separate violations in case of an invalid e-mail.
+    //   Unifiy field item and field property constraints.
     $violations = $user->validate();
-    $this->assertEqual(count($violations), 1, 'Violation found when email is too long');
+    $this->assertEqual(count($violations), 2, 'Violations found when email is too long');
     $this->assertEqual($violations[0]->getPropertyPath(), 'mail.0.value');
-    $this->assertEqual($violations[0]->getMessage(), t('This value is not a valid email address.'));
+    $this->assertEqual($violations[1]->getMessage(), t('This value is not a valid email address.'));
 
     // Provoke a e-mail collision with an exsiting user.
     $user->set('mail', 'existing@exmaple.com');