Add multiple fields in to single target fields using UDF

Hi Team,

I have to add fields’ value in to target single field. I cannot use “add” because it does not work for empty value and I can also not add”mapwithdefault”. I am using SAP PI 7.1. Could you please suggest if there is any UDF for this.

Source Structure:

Source1

          Field1

         Field2

         Field3

         Field4

Source2

          Field12

         Field22

         Field32

         Field42

There are two source nodes, two Idoc will be generated in my scenario. I have to add Field1, Field2 & Field3 in to target single Idoc field. And same for Source2 for another Idoc.

Thanks in advance for your response!

Kumar