How to customize a select menu's #empty_option

/**
 * Implements hook_webform_element_alter().
 */
function MODULE_webform_element_alter(array &$element, \Drupal\Core\Form\FormStateInterface $form_state, array $context) {
  if (in_array($element['#type'], ['select', 'webform_select_other', 'webform_select_term', 'webforn_entity_select']) && !isset($element[ '#empty_option'])) {
    if (!empty($element['#multiple'])) {
      $element['#empty_option'] = empty($element['#required']) ? t('- Select -') : t('- None -');
    }
    else {
      $element['#empty_option'] = empty($element['#required']) ? t('- None -') : NULL;
    }
  }
}

@see https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Render%21Element%21Select.php/class/Select