diff -u b/core/modules/options/lib/Drupal/options/Plugin/field/widget/ButtonsWidget.php b/core/modules/options/lib/Drupal/options/Plugin/field/widget/ButtonsWidget.php
--- b/core/modules/options/lib/Drupal/options/Plugin/field/widget/ButtonsWidget.php
+++ b/core/modules/options/lib/Drupal/options/Plugin/field/widget/ButtonsWidget.php
@@ -69,7 +69,7 @@
    */
   protected function getEmptyOption() {
     if (!$this->required && !$this->multiple) {
-      return self::OPTIONS_EMPTY_NONE;
+      return static::OPTIONS_EMPTY_NONE;
     }
   }
 
diff -u b/core/modules/options/lib/Drupal/options/Plugin/field/widget/OptionsWidgetBase.php b/core/modules/options/lib/Drupal/options/Plugin/field/widget/OptionsWidgetBase.php
--- b/core/modules/options/lib/Drupal/options/Plugin/field/widget/OptionsWidgetBase.php
+++ b/core/modules/options/lib/Drupal/options/Plugin/field/widget/OptionsWidgetBase.php
@@ -199,7 +199,7 @@
    * Returns the empty option to add to the list of options, if any.
    *
    * @return string|null
-   *   Either self::OPTIONS_EMPTY_NONE, self::OPTIONS_EMPTY_SELECT, or NULL.
+   *   Either static::OPTIONS_EMPTY_NONE, static::OPTIONS_EMPTY_SELECT, or NULL.
    */
   protected function getEmptyOption() { }
 
diff -u b/core/modules/options/lib/Drupal/options/Plugin/field/widget/SelectWidget.php b/core/modules/options/lib/Drupal/options/Plugin/field/widget/SelectWidget.php
--- b/core/modules/options/lib/Drupal/options/Plugin/field/widget/SelectWidget.php
+++ b/core/modules/options/lib/Drupal/options/Plugin/field/widget/SelectWidget.php
@@ -66,7 +66,7 @@
     if ($this->multiple) {
       // Multiple select: add a 'none' option for non-required fields.
       if (!$this->required) {
-        return self::OPTIONS_EMPTY_NONE;
+        return static::OPTIONS_EMPTY_NONE;
       }
     }
     else {
@@ -74,10 +74,10 @@
       // and a 'select a value' option for required fields that do not come
       // with a value selected.
       if (!$this->required) {
-        return self::OPTIONS_EMPTY_NONE;
+        return static::OPTIONS_EMPTY_NONE;
       }
       if (!$this->has_value) {
-        return self::OPTIONS_EMPTY_SELECT;
+        return static::OPTIONS_EMPTY_SELECT;
       }
     }
   }
diff -u b/core/modules/options/options.module b/core/modules/options/options.module
--- b/core/modules/options/options.module
+++ b/core/modules/options/options.module
@@ -8,6 +8,7 @@
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\field\FieldUpdateForbiddenException;
+use Drupal\options\Plugin\field\widget\OptionsWidgetBase;
 
 /**
  * Implements hook_help().
@@ -451,8 +452,10 @@
  *
  * @param $variables
  *   An associative array containing:
- *   - option: A string representing the option that should be displayed.
- *     Either 'option_none' or 'option_select'.
+ *   - option: A string representing the option that should be displayed. Either
+ *     \Drupal\options\Plugin\field\widget\OptionsWidgetBase::OPTIONS_EMPTY_NONE
+ *     or
+ *     \Drupal\options\Plugin\field\widget\OptionsWidgetBase::OPTIONS_EMPTY_SELECT.
  *   - widget: The widget object requesting the option.
  *   - instance: The instance definition.
  *
@@ -469,7 +472,7 @@
       break;
 
     case 'options_select':
-      $output = ($option == 'option_none' ? t('- None -') : t('- Select a value -'));
+      $output = ($option == OptionsWidgetBase::OPTIONS_EMPTY_NONE ? t('- None -') : t('- Select a value -'));
       break;
   }