How can I allow reviews with no comment in WordPress?

 
add_filter('allow_empty_comment','wpsc_myprefix_allow_empty_review',10,2);
function wpsc_myprefix_allow_empty_review($allow,$commentdata){	
	if(!empty($_POST['geodir_overallrating']) && empty($_POST['comment_parent'])){
		$allow = true;
	}	
	return $allow;
}