An optional field without extra spacing

[Remillard]

I've been trying to figure out a way to have an optional field. For instance

task ${2:lifetime} ${1:taskname} (
    $0
);

endtask : $1

Field 2 is optional, but I do want it to be present in case it's required. When the snippet expands, lifetime is presented and there are spaces around it. If I type in the name, then tab, I'm highlighting lifetime. If I hit C-d it erases lifetime and I can then tab and go to the $0 position, however the location of field 2 has two spaces now.

I've tried: task ${2:lifetime }${1:taskname} ( which works a little better if deleted, however then does require that the user then hit space after they type the lifetime keyword desired.

I fiddled with an ELisp transformation but couldn't quite find anything that would transform only after the whole word was typed in (for example ${2:lifetime $(concat yas-text " ")} operated after every key and was really wrong.

Any ideas on how to accomplish an optional field that will not leave a blank space?

[georgtree]

I faced with the same issue, and would like to see the solution