New Post: error on get Attributes[].Value

<a title="one-punch-man-ep-01-viet-sub" data-episode-tap="01" data-episode-id="127345" data-type="watch" class="" href="http://anime47.com/xem-phim-one-punch-man-ep-01/127345.html"><b>01</b></a>

<a title="one-punch-man-ep-02-viet-sub" data-episode-tap="02" data-episode-id="128858" data-type="watch" class="active" href="http://anime47.com/xem-phim-one-punch-man-ep-02/128858.html"><b>02</b></a>

C#

var eplist = doc.DocumentNode.SelectNodes("//li").ToList();
foreach (var item_ep in eplist)
{
doc.LoadHtml(item_ep.InnerHtml);
doc.DocumentNode.SelectNodes("//b")[0].InnerText; -> work
doc.DocumentNode.SelectNodes("//a")[0].Attributes["data-episode-id"].Value; -> work
doc.DocumentNode.SelectNodes("//a")[0].Attributes["href"].Value; -> get error in doc.LoadHtml(item_ep.InnerHtml);
}

how to fix it?
thank everyone.