public function thumbnail($icon, $icon2 = null, $width = null, $height = null)
    {
        $this->thumbnail = trim($icon);

        if (! str_empty($icon2)) {
            $this->thumbnail2 = trim($icon2);
        }

        if (! is_null($width)) {
            $this->thumbnailWidth = $width;
        }

        if (! is_null($height)) {
            $this->thumbnailHeight = $height;
        }

        return $this;
    }