`map_extract` returns `[NULL]` instead of `[]` for missing keys

[neilconway]

Describe the bug

The docs for map_extract say that it returns an empty list if the requested key is not present in the map, but that is not the implemented behavior: [NULL] is returned instead. This behavior does not match how map_extract behaves in DuckDB; it also makes it impossible to distinguish between an absent key and a key whose associated value is NULL, which is arguably the point of having map_extract return a list in the first place.

To Reproduce

SELECT
    map_extract(MAP {'a': 1, 'b': NULL}, 'a') AS present,
    map_extract(MAP {'a': 1, 'b': NULL}, 'b') AS present_null,
    map_extract(MAP {'a': 1, 'b': NULL}, 'c') AS missing,
    element_at(MAP {'a': 1, 'b': NULL}, 'c') AS alias_missing;

Verified using DataFusion CLI 55.0.0 and DuckDB v1.5.5:

Engine	present	present_null	missing	alias_missing
DataFusion	[1]	[NULL]	[NULL]	[NULL]
DuckDB	[1]	[NULL]	[]	[]

Expected behavior

map_extract should return [] for a missing key.

Additional context

No response

[neilconway]

take