UDJE, two-word field

Hello.
I know it looks stupid but how to use a two-word fields in UDJE?
For example I have fields: "Full Name" and "Nick" and I want to to join them (or some other operation). I tried "Full Name"+Nick, (Full Name"+Nick), [Full Name]+Nick etc.. and nothing didnt work.
I was solving this by renaming 2 word names to 1 word name ("Full Name" > "FullName") :o
I was searching about it and didnt find anything so sorry about this stupdi question.

Thanks