/**
* Adds the given graph or triple as an optional condition.
*
* @since 0.3
*
* @param string|GraphBuilder $subject
* @param string|null $predicate
* @param string|null $object
* @return self
* @throws InvalidArgumentException
*/
public function optional($subject, $predicate = null, $object = null)
{
$this->graphBuilder->optional($subject, $predicate, $object);
return $this;
}
