mapp from document to variable does not work

I have a flow document object on pipline which I can see it with debugger on pipline:
I am going to do easy thing, mapp the ns6:Code to a variable name myCode. So
i mapp this document above to other document named MyCopyDocument with the same structure and I can see this document on pipline too:
Now I mapp the ns6:Code to my varable myCode but in debugger the variable myCode is not visible (becuse is empty)
do you have any idea?

Please double check that

  1. All segments in /ns4:Invoice/ns2:content/ns2:subcontent/ns3:Header are really IData’s
  2. ns6:Code is really a string.

Do this by saving the pipeline.

Designer can display structures which are not IData, but mapping does not work with them.

It seems it was misunderstanding the branch part of my code !
I mistakenly tried with default and null in a branch and could not check the right value for the parameter on pipline.
Thanks for your reply and help