Mapping question

I have a source with a node and sub node under it and mapped as follows :

Here for all the source fields I have chnaged the context  to 'Test_source_msg'.

But when Iam not getting results as expected.

I want 'tg_fld1' to have value 'A'.

If you see in the first instance I don't have subnode present, I can have cases where sub node can not be present entirely. I think this is causing the issue when I debug.

I'm not comfortable with Java, I want to do this with mapping instead on UDF.

Thanks in advance.