Field::appendFetchDataModifier

protected function appendFetchDataModifier($modifier)
{
	if (!is_callable($modifier))
	{
		throw new SystemException(sprintf(
			'Modifier of "%s" field of "%s" entity should be a callback',
			$this->name, $this->entity->getDataClass()
		));
	}

	$this->fetchDataModifiers[] = $modifier;
}