I have a scenario where I get an XML, I am using queryXMLNode and mapping the xml element value to IS document. When I get a null value in one node, I want to get the value from other node which will be always has value. Please advise how to do this.

Here you can use step like pub.xml:getXMLNodeIterator and pass the node name in criteria field.If the result is true then you can convert node to document else you can again make query with other node.

Thanks
Baharul