title: "Null" is null or not an object error in IE javascript
body: <p>The following code executes fine in Firefox and Chrome, but gives an error:</p>
  
  <pre><code>'null' is null or not an object
  </code></pre>
  
  <p>when executed in Internet Explorer.</p>
  
  <pre><code>if (xmlhttp.responseXML != null)
      {
      var xmlDoc = xmlhttp.responseXML.documentElement ;
      var ResultNodes = xmlDoc.getElementsByTagName ("Result") ;   &lt;---- error here
      if (ResultNodes != null)
          {
  </code></pre>
  
  <p>(I would have thought the line after the one indicated would be more likely to return the error but the debugger says the run-time error is at the line indicated) </p>
  
  <p>Any ideas why?</p>