Join the HTML rows.

def render(self, rows):
        """
        Join the HTML rows.
        """
        if not rows:
            return ''

        li_tags = mark_safe(u"\n".join(format_html(u'<li>{0}</li>', force_text(row)) for row in rows))
        if self.title:
            return format_html(u'<div class="toolbar-title">{0}</div>\n<ul>\n{1}\n</ul>', self.title, li_tags)
        else:
            return format_html(u'<ul>\n{0}\n</ul>', li_tags)