public function getFirstValueNode(Node $node = null, $property, Node $default = null) {
        $valueFromNode = $this->getFirstValue($node, $property, $default);
        if ($valueFromNode == $default)
            return $default;
        
        if (is_a($valueFromNode, 'ML\JsonLD\Node'))
            return $valueFromNode;
        else
            return $default;
    }