[BUG] not ignore null in ARRAY_AGG with `DISTINCT` and `IGNORE NULLS`

[davidlghellin]

Describe the bug

When using array_agg (or ARRAY_AGG) with both DISTINCT and IGNORE NULLS clauses, the IGNORE NULLS clause is not being respected. NULL values are included in the result even when they should be filtered out.

To Reproduce

SELECT ARRAY_AGG(DISTINCT x IGNORE NULLS) as result
FROM (VALUES (1), (2), (NULL), (2), (NULL), (1)) AS t(x);

Expected behavior

> SELECT ARRAY_AGG(DISTINCT x IGNORE NULLS) as result
FROM (VALUES (1), (2), (NULL), (2), (NULL), (1)) AS t(x);
+--------+
| result |
+--------+
| [2, 1]  |
+--------+

Additional context

DISTINCT and IGNORE NULLS

IGNORE NULLS

Testing ibis from Sail
lakehq/sail#1187

[xanderbailey]

> CREATE TABLE test_table (x INT);
0 row(s) fetched.
Elapsed 0.008 seconds.

> INSERT INTO test_table VALUES (1), (2), (NULL), (2), (NULL), (1);
+-------+
| count |
+-------+
| 6     |
+-------+
1 row(s) fetched.
Elapsed 0.010 seconds.

> SELECT ARRAY_AGG(DISTINCT x IGNORE NULLS ORDER BY x) as result FROM test_table;
+--------+
| result |
+--------+
| [1, 2] |
+--------+
1 row(s) fetched.
Elapsed 0.009 seconds.

> SELECT ARRAY_AGG(DISTINCT x IGNORE NULLS) as result FROM test_table;
+--------------+
| result       |
+--------------+
| [2, NULL, 1] |
+--------------+
1 row(s) fetched.
Elapsed 0.008 seconds.

So this is working with the ORDER BY