diff --git a/core/lib/Drupal/Core/Field/FieldDefinitionInterface.php b/core/lib/Drupal/Core/Field/FieldDefinitionInterface.php
index 5e00f7e..e4f47b2 100644
--- a/core/lib/Drupal/Core/Field/FieldDefinitionInterface.php
+++ b/core/lib/Drupal/Core/Field/FieldDefinitionInterface.php
@@ -160,6 +160,25 @@ public function isDisplayConfigurable($display_context);
   public function getDisplayOptions($display_context);
 
   /**
+   * Returns whether the field can be empty.
+   *
+   * If a field is required, an entity needs to have at least a valid,
+   * non-empty item in that field's FieldItemList in order to pass validation.
+   *
+   * An item is considered empty if its isEmpty() method returns TRUE.
+   * Typically, that is if at least one of its required properties is empty.
+   *
+   * @return bool
+   *   TRUE if the field is required.
+   *
+   * @see \Drupal\Core\TypedData\Plugin\DataType\ItemList::isEmpty()
+   * @see \Drupal\Core\Field\FieldItemInterface::isEmpty()
+   * @see \Drupal\Core\TypedData\DataDefinitionInterface:isRequired()
+   * @see \Drupal\Core\TypedData\TypedDataManager::getDefaultConstraints()
+   */
+  public function isRequired();
+
+  /**
    * Returns the default value for the field in a newly created entity.
    *
    * @param \Drupal\Core\Entity\FieldableEntityInterface $entity
diff --git a/core/modules/field_ui/src/Form/FieldConfigEditForm.php b/core/modules/field_ui/src/Form/FieldConfigEditForm.php
index 1cf796e..866ff9a 100644
--- a/core/modules/field_ui/src/Form/FieldConfigEditForm.php
+++ b/core/modules/field_ui/src/Form/FieldConfigEditForm.php
@@ -35,20 +35,18 @@ class FieldConfigEditForm extends EntityForm {
   public function form(array $form, FormStateInterface $form_state) {
     $form = parent::form($form, $form_state);
 
-    /** @var \Drupal\field\Entity\FieldConfig $field */
-    $field = $this->entity;
-    $field_storage = $field->getFieldStorageDefinition();
+    $field_storage = $this->entity->getFieldStorageDefinition();
     $bundles = $this->entityManager->getBundleInfo($this->entity->getTargetEntityTypeId());
 
     $form_title = $this->t('%field settings for %bundle', array(
-      '%field' => $field->getLabel(),
-      '%bundle' => $bundles[$field->getTargetBundle()]['label'],
+      '%field' => $this->entity->getLabel(),
+      '%bundle' => $bundles[$this->entity->getTargetBundle()]['label'],
     ));
     $form['#title'] = $form_title;
 
     if ($field_storage->isLocked()) {
       $form['locked'] = array(
-        '#markup' => $this->t('The field %field is locked and cannot be edited.', array('%field' => $field->getLabel())),
+        '#markup' => $this->t('The field %field is locked and cannot be edited.', array('%field' => $this->entity->getLabel())),
       );
       return $form;
     }
@@ -57,7 +55,7 @@ public function form(array $form, FormStateInterface $form_state) {
     $form['label'] = array(
       '#type' => 'textfield',
       '#title' => $this->t('Label'),
-      '#default_value' => $field->getLabel() ?: $field_storage->getName(),
+      '#default_value' => $this->entity->getLabel() ?: $field_storage->getName(),
       '#required' => TRUE,
       '#weight' => -20,
     );
@@ -65,7 +63,7 @@ public function form(array $form, FormStateInterface $form_state) {
     $form['description'] = array(
       '#type' => 'textarea',
       '#title' => $this->t('Help text'),
-      '#default_value' => $field->getDescription(),
+      '#default_value' => $this->entity->getDescription(),
       '#rows' => 5,
       '#description' => $this->t('Instructions to present to the user below this field on the editing form.<br />Allowed HTML tags: @tags', array('@tags' => $this->displayAllowedTags())) . '<br />' . $this->t('This field supports tokens.'),
       '#weight' => -10,
@@ -74,18 +72,18 @@ public function form(array $form, FormStateInterface $form_state) {
     $form['required'] = array(
       '#type' => 'checkbox',
       '#title' => $this->t('Required field'),
-      '#default_value' => $field->isRequired(),
+      '#default_value' => $this->entity->isRequired(),
       '#weight' => -5,
     );
 
     // Create an arbitrary entity object (used by the 'default value' widget).
     $ids = (object) array(
       'entity_type' => $this->entity->getTargetEntityTypeId(),
-      'bundle' => $field->getTargetBundle(),
+      'bundle' => $this->entity->getTargetBundle(),
       'entity_id' => NULL
     );
     $form['#entity'] = _field_create_entity_from_ids($ids);
-    $items = $form['#entity']->get($field->getName());
+    $items = $form['#entity']->get($this->entity->getName());
     $item = $items->first() ?: $items->appendItem();
 
     // Add field settings for the field type and a container for third party