InfoPath Dev

In Infopath 2003 I have added the web service as my secondary data source. It has a query field call tmsSummaryId(its int64). It is a parameter of my web service method.

I am trying to query the web service using user Input

I wrote following code.

public void CTRL1_23_OnClick(DocActionEvent e)
        {
           
                // Write your code here.
                IXMLDOMNode filed6 = thisXDocument.DOM.selectSingleNode("//my:field6");
                IXMLDOMDocument2 domXml = (IXMLDOMDocument2)thisXDocument.DataObjects["GetCustomerData"].DOM;
                domXml.setProperty("SelectionNamespaces", "xmlns:dfs='http://schemas.microsoft.com/office/infopath/2003/dataFormSolution' xmlns:ns1=' http://localhost:6548/BusinessServices'");
                IXMLDOMNode queryField = domXml.selectSingleNode("/dfs:myFields/dfs:queryFields");
                //IXMLDOMNode queryField = domXml.selectSingleNode("/dfs:myFields/dfs:dataFields/GetCustomerDataResponse/GetCustomerDataResult/ParentName");
                //filed2.text = queryField.nodeValue;
                queryField.text =field6.text;

                thisXDocument.DataObjects["GetCustomerData"].Query();
           
           
           
        }

when the executing the Query() method is giving an error calling

System.NullReferenceException: Object reference not set to an instance of an object

Can any one please help on this