Template:~targ
From Maths
Purpose
If we write {{{1|{{{2|}}}}}} this becomes 2 only if 1 is completely absent, if we call this template as ...|1=|2=stuff}} then this will become "" (empty string) as 1 is set, it's just empty.
In this case you would use:
- {{~targ|1={{{1|}}}|2={{{2|}}}}} which evaluates to its 2nd input if 1 is empty