`FILTER` does not handle NULLs correctly

[neilconway]

Describe the bug

> SELECT g, COUNT(a) FILTER (WHERE b < 1) AS count_a
FROM (VALUES (0, 1, CAST(NULL AS INT)), (0, 2, 2)) AS t(g, a, b)
GROUP BY g;
+---+---------+
| g | count_a |
+---+---------+
| 0 | 1       |
+---+---------+
1 row(s) fetched.
Elapsed 0.016 seconds.

This is incorrect; Postgres returns 0, 0 because no rows pass the filter. DF looks at the two-valued boolean result of the filter (true/false) and doesn't check the NULL bitmap.

To Reproduce

No response

Expected behavior

No response

Additional context

No response

[neilconway]

take

[cetra3]

This, like other semantics in DF, I think are OK in some scenarios? Why are we needing to align with PostgreSQL semantics everywhere? What do other systems like DuckDB and the like do.