10.x: docs: name the two known differences 10.2.0 ships with — value set Union/Remove over NULL (#360) and RangeLowerBoundComparer in a query (#385) #397

Problem

10.2.0 ships with two known silent differences between a query and the same LINQ over the loaded rows. Both are deferred from 10.2.0 (#358), and the docs don't mention either:

• Value set Union is declared NULL only for a NULL operand, but array_cat isn't strict: a filter and a projection disagree on a NULL column #360 → port 10.x: value set Union and Remove over a NULL operand project a value instead of NULL (port of #360) #395: a value set Union or Remove over a NULL operand returns a value in a projection, where a filter treats it as NULL. Reachable from a nullable column and from the optional side of an outer join.
• RangeLowerBoundComparer.Compare runs as SQL in the range order: EF Core rewrites any Compare(a, b) to the natural comparison #385 → port 10.x: RangeLowerBoundComparer.Compare in a query runs in the range order (port of #385) #396: RangeLowerBoundComparer<TRange, T>.Compare (and RangeSet<TRange, T>.LowerBoundComparer) in a query compares in the range order, not by lower bound. EF Core rewrites any Compare(a, b) this way (Any method named Compare is translated as the natural comparison of its arguments, so a comparer's own ordering is silently ignored (StringComparer.OrdinalIgnoreCase, custom IComparer<T>) dotnet/efcore#39402).

Both were measured on release/10.x on EF Core 10.0.0 and 10.0.13 (see the port issues).

Change

On release/10.x only, in docs/efcore.md#what-runs-where: a short "known differences" part naming each case, the workaround, and the issue that fixes it.

• Union/Remove: test the operand for null yourself, x == null ? null : x.Union(y). Measured: the projection then returns NULL, and a filter is unchanged.
• The comparer: compare loaded rows (AsEnumerable()), as for the other in-memory members.

docs/ranges.md#sort-ranges-the-way-a-set-does links the comparer entry. main gets neither: both fixes land there before 11.0.0. Each port (#395, #396) removes its entry.

Release

A docs entry under ## [10.2.0] in the changelogs it touches. Fixed only on release/10.x, so close it by hand (#365).