Not true… this is what plus item / minus item are for (I think there’s also an :add and :remove list version of those operators, too). Just like you can do a = a+1 if a is an int (but currently empty), you can also do a_list = a_list:add item another_item (even if a_list is empty). That’s the reason for these (what may seem mysterious) list operators. See my video about Amazon Product API – see around the 16 minute mark here:
Edit: some further info. I did just go suss this out and (as in RGs) custom states that are lists have :plus item and :minus item (basically push and pop a single element of the correct type), but do not have operators called “:plus list” / “:minus list” feature.
HOWEVER, you will note that merged with is available in such expressions. So that’s the equivalent of a “:plus list” item (which, in the typical Bubble way, would not allow dupes).
ALSO, :filtered by Advanced is available… so you can use that as a proxy for “:minus list”.
So, if you have some-list-of-texts (for example) and some-other-list-of-texts, you can do:
“Add one item to the list” (to subtract one item use :minus item):
“Add one list to another”:
“Subtract items from another list from current list”:
The nomenclature is obtuse, but the functionality is there!