query InfoPaht nodes

secDSNav.Select("/dfs:myFields/dfs:dataFields/d:SharePointListItem_RW[d:EXPRTN_DT!='']", NamespaceManager);

secDSNav.Select("/dfs:myFields/dfs:dataFields/d:SharePointListItem_RW/d:EXPRTN_DT[not(text())]", NamespaceManager)