[Bertrand]

I'm trying to add the pubdate to every book when I save to disk :
For now, my template is as follow :
{author_sort[0]}/{author_sort} - {series}{series_index:0>2s| | - } {title} ({pubdate})

which gives : D/Doe, John/Title (2021)

But, obviously, some books have no pubdate, and I get this :

B/Bench, John/Title of the book (101)

(What is this "101" number ?)

So my goal is :
if pubdate = 101 do nothing
else add "(pubdate)"

I have tried various variations based on the series model but I can't get anywhere.

Thanks for your help.