NULL semantics, v0.1.0 docs, PLOMID

Classification: Supported behavior (verified in the executor's expression, comparison, and row-equality paths).

Case	Result
`NULL = NULL`, `NULL <> 1`, `NULL < 1`	`NULL`
`WHERE NULL` / `WHERE <null predicate>`	row filtered (only `Bool(true)` passes; `Equal` special-cases NULL→false)
`NOT NULL`	`NULL`
`NULL AND TRUE`	`false` here (differs from strict 3VL where it is NULL) — implementation uses is-true checks
`x IN (…, NULL)` no match	`NULL`; match → `true`
`BETWEEN/LIKE/comparison` with NULL	`NULL`
`IS NULL / IS NOT NULL`, `IS DISTINCT FROM`	NULL-aware (`NULL IS DISTINCT FROM NULL → false`)
`IS TRUE/FALSE/UNKNOWN`	three-valued test
`IS JSON` with NULL	`NULL`; invalid text → `false`
Aggregates	skip NULL except `COUNT(*)`; `SUM/AVG/MIN/MAX` empty → NULL; `json_agg` keeps NULL as JSON null
`concat` / `concat_ws`	`concat` skips NULLs; `concat_ws` skips NULL args, NULL sep → NULL
`ORDER BY`	default `ASC→NULLS LAST`, `DESC→NULLS FIRST`; overridable
Missing JSON field	NULL (see JSON)

sqlsource

SELECT NULL = NULL;            -- NULL
SELECT 1 WHERE NULL;           -- zero rows
SELECT count(*), count(nick) FROM users;
SELECT * FROM t ORDER BY x;    -- NULLS LAST

Common mistake: WHERE col = NULL never matches — use WHERE col IS NULL.

NULL semantics

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