code: public function getCustomFieldByType($type)
      {
          if (isset($this->servicesByType[$type])) {
              return $this->servicesByType[$type];
          } else {
              throw new \LogicException('the custom field with type '.$type.' '
                  . 'is not found');
          }
      }
docs: Get a custom field stored in the provider. The custom field is identified
  by its type.
  
  @param string $type The type of the wanted service
  @return CustomFieldInterface