AJAX how to return Null values

When using responseXML to return values from an asp document it will not return a NULL value or a blank value from the database without holding up the responseXML. How can I properly handle Null values without having to have somthing in the database field.  Right now I must have a value in the database field or the AJAX script does not complete the script. So how can  XML / AJAX ignore  the Nulls.

THE FOLLOWING IS THE AJAX:

function GetSystemEdit(SysID)
{
        
         xmlHttp = GetXmlHttpObject();
                       xmlHttp.onreadystatechange = ReturnGetSystem;
        xmlHttp.open('Get','EstimatesASP.asp?action=OpenSystem&SysID='+SysID, true);
        xmlHttp.send(null);
}


function ReturnGetSystem()
{

 if (xmlHttp.readyState == 4)
        {
             
            if (xmlHttp.status == 200)
          {
                    
                  var xmlDoc = xmlHttp.responseXML.documentElement;
                  
                  var System = xmlDoc.getElementsByTagName('System')[0].childNodes[0].nodeValue;
                  var DateEntered = xmlDoc.getElementsByTagName('DateEntered')[0].childNodes[0].nodeValue;
                var EnteredBy = xmlDoc.getElementsByTagName('EnteredBy')[0].childNodes[0].nodeValue;
                  var Notes = xmlDoc.getElementsByTagName('Notes')[0].childNodes[0].nodeValue;
                  var RCSNotes = xmlDoc.getElementsByTagName('RCSNotes')[0].childNodes[0].nodeValue;
                  var TaxRate = xmlDoc.getElementsByTagName('TaxRate')[0].childNodes[0].nodeValue;
                  var MU = xmlDoc.getElementsByTagName('MU')[0].childNodes[0].nodeValue;
                  var SysID = xmlDoc.getElementsByTagName('SysID')[0].childNodes[0].nodeValue;
                  

         }
             else
             {
            alert('There was a problem with the request.');
         }
      }
        
}







THE FOLLOWING IS THE ASP CODE:

Dim EstID
Dim XML
Dim System
Dim DateEntered
Dim EnteredBy
Dim TaxRate
Dim MU


SysID = CStr(Request.QueryString("SysID"))


XML = ""
     

      SQL = "SELECT * FROM Systems WHERE SystemID = "&SysID
      set rs=Server.CreateObject("ADODB.Recordset")
      rs.Open SQL, REDconnstring
      
      
      XML = XML + "<root>"      
      XML = XML + "<System>"&rs("System")&"</System>"
      XML = XML + "<DateEntered>"&rs("DateEntered")&"</DateEntered>"
      XML = XML + "<EnteredBy>"&rs("EnteredBy")&"</EnteredBy>"
      XML = XML + "<Notes>"&rs("Notes")&"</Notes>"
      XML = XML + "<RCSNotes>"&rs("RCSNotes")&"</RCSNotes>"
      'XML = XML + "<DateBid>"&rs("DateBid")&"</DateBid>"
      'XML = XML + "<DateWon>"&rs("DateWon")&"</DateWon>"
      XML = XML + "<TaxRate>"&rs("TaxRate")&"</TaxRate>"
      XML = XML + "<MU>"&rs("MU")&"</MU>"
      XML = XML + "<SysID>"&SysID&"</SysID>"
                     XML = XML + "</root>"


      
    set rs = nothing
      response.ContentType = "text/xml"
      response.Write(XML)




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