code: private function _cacheCustomFieldsGroup(CustomFieldsGroup $group)
      {
          foreach ($group->getCustomFields() as $field) {
              $this->cache[$group->getEntity()][$field->getSlug()] = $field;
          }
      }
docs: Set in cache of the custom fields of a customfield Group.
  
  @param CustomFieldsGroup $group The given CustomFieldsGroup