I don’t have plans on booting up the laptop today, but if I do I’ll give it a shot. Fortunately you can find examples of this if you search ‘design script if’ on the forum: Workaround with If statement and empty list - #7 by jacob.small
I think you may have inverses the input variables in your example - there is an ‘x’ instead of an ‘a’ or vice versa. Not sure if that will resolve though.
My thought on the list.first item was to just use that line of design script, or the List.FirsItem node. Not sure that an if statement is needed.