Don't parse empty Bb Codes (default ones)

    public function renderValidTag(array $tagInfo, array $tag, array $rendererStates)
    {
        $parent = parent::renderValidTag($tagInfo, $tag, $rendererStates);

        if( isset($tag['tag'])
            && in_array($tag['tag'], array('b', 'i', 'u', 's', 'color', 'font', 'size', 'left', 'center', 'right', 'indent', 'url', 'email', 'img', 'quote', 'code', 'php', 'html', 'plain', 'media', 'attach'))
        )
        {
            $content = $this->renderSubTree($tag['children'], $rendererStates);
            if(empty($content))
            {
                return $this->renderInvalidTag($tag, $rendererStates);
            }
        }

        return $parent;
    }