Hi Myki, here is the solution ! (yes i love to talk to myself, even if i'm not always agree with myself
).
Code:
{authors:'switch(count($, '&'), 1, $, list_item($, 0, '&'))'}{series:| - |}
If {series} is empty, the custom field will be feed with the first author only,
If {series} is not empty, the custom field will be feed with the first author, a "-", a space and the name of the serie.
ex : Rowling, JK - Harry Potter
(yes i love myself
)