/**
  * Adds a SettingsField to this SettingsSection if it does not already exist.
  *
  * @since 3.0.0
  *
  * @param SettingsField $field The SettingsField object to add to the section.
  * @return void
  */
 private function addField(SettingsField $field)
 {
     $fieldSlug = $field->getSlug();
     if (array_key_exists($fieldSlug, $this->settingsFields)) {
         wp_die(__("A field with ID {$fieldSlug} was already added to the settings section {$this->getSlug()}.", parent::$textDomain));
     } else {
         $this->settingsFields[$fieldSlug] = $field;
     }
 }