public function setShadow()
    {
        $args = func_get_args();

        if (isset($args[0]) && ($args[0] instanceof MarkerImage)) {
            if ($args[0]->getUrl() === null) {
                throw OverlayException::invalidMarkerShadowUrl();
            }

            $this->shadow = $args[0];
        } elseif (isset($args[0]) && is_string($args[0])) {
            if ($this->shadow === null) {
                $this->shadow = new MarkerImage();
            }

            $this->shadow->setUrl($args[0]);
        } elseif (!isset($args[0])) {
            $this->shadow = null;
        } else {
            throw OverlayException::invalidMarkerShadow();
        }
    }