title: HTML Agility Pack Null Reference
body: <p>I've got some trouble with the HTML Agility Pack.</p>
  
  <p>I get a null reference exception when I use this method on HTML not containing the specific node. It worked at first, but then it stopped working. This is only a snippet and there are about 10 more foreach loops that selects different nodes.</p>
  
  <p>What am I doing wrong?</p>
  
  <pre><code>public string Export(string html)
  {
      var doc = new HtmlDocument();
      doc.LoadHtml(html);
      // exception gets thrown on below line
      foreach (var repeater in doc.DocumentNode.SelectNodes("//table[@class='mceRepeater']"))
      {
          if (repeater != null)
          {
              repeater.Name = "editor:repeater";
              repeater.Attributes.RemoveAll();
          }
      }
  
      var sw = new StringWriter();
      doc.Save(sw);
      sw.Flush();
  
      return sw.ToString();
  }
  </code></pre>