Calling method from catch method doesn't work

I'm trying to call a method from a catch block but the xmlnode inside the method doesn't seem to work. I'm getting a null. If I call the same method from the try block it works.

var doc = new XmlDocument();

try
{

 doc.Load(f.FullPath);
// do some work 

}

 catch (Exception e)
 {
  if (e is XMLException)
  {
   checkXML(ref doc);
  }

public void checkXML(ref XmlDocument doc)
            {

                XmlNode xn = doc.SelectSingleNode("/BroadcastMonitor/Current");
                xn["name1"].InnerText = SecurityElement.Escape(xn["name1"].InnerText);
                xn["name2"].InnerText = SecurityElement.Escape(xn["name2"].InnerText); ;


            }

Now when the catch block calls method 'checkXML', i get xn as null. But if I execute the same from the 'try' block just to check, 'xn' has a value. 'doc' too has a value regardless of when called try or from catch block.

Why is this happening? Please help me understand.

Thank you.