RangeIntersectAgg returns empty over a sequence holding a null range, where range_intersect_agg skips the NULL; RangeAgg throws #361

Problem

docs/ranges.md#aggregate-a-sequence-of-ranges calls RangeAgg() and RangeIntersectAgg() "the in-memory versions of PostgreSQL's range_agg and range_intersect_agg". Those skip NULL inputs, as SQL aggregates do, and so do LINQ's aggregates over nullable values (new int?[] { null, 3, 1 }.Min() is 1). The in-memory RangeAgg and RangeIntersectAgg don't. Measured 2026-10-24 on PostgreSQL 16, with a nullable DateRange column holding NULL, [2026-03-01,2026-03-10], [2026-03-05,2026-03-25] and NULL, in GroupBy(r => 1).Select(g => g.Select(r => r.Maybe!).…):

RangeIntersectAgg treats a null range as one that intersects to empty. RangeAgg hands the null to the sort and fails there; with #356's check it would fail with ArgumentNullException instead.

Change

Rule (c) on #350, extended to aggregates: RangeAgg and RangeIntersectAgg skip null ranges, as SQL and LINQ's nullable aggregates do. Over nothing but nulls they return what they return over an empty sequence, which must match SQL's NULL (RangeIntersectAgg returns null today; check RangeAgg). This is in memory only; the SQL is already right.

silent for RangeIntersectAgg; the RangeAgg half turns a throw into a value. A 10.x minor can carry it under ### Changed answers.

Done when

RangeAggregateParityTests runs both aggregates over a nullable column holding NULLs among other shapes, for every family, and compares with memory.