Use pydantic pattern for non-hashable default values (i.e. lists)

[basedBaba]

closes #2543

Checklist

• No CHANGELOG update needed

• No new tests needed

• No documentation update needed

[williballenthin]

i think there's a conceptual difference between an empty list and None. None indicates that we don't have the data, while the empty list shows we have the data but there was nothing in it.

[basedBaba]

Ah yes, I understand your point. According to #2537 (comment), I thought the intention behind this issue was to avoid checks for such fields (as None and [] both have a truth value of False) and to use the same pattern throughout the code.
(Really sorry for the late response and re-review mis-click as well)