[Deferred] Revisit: null-propagation semantics for complex-property navigation (#221 decision)

[savasp-agent]

Type: Task · Status: deferred (tracked for future revisit, not scheduled)

Purpose

@savasp decided (#221, 2026-07-10) to ratify the null-propagation semantics for complex-property navigation — p.Address.City == null matches owners with no Address node as well as owners whose City is literally null; projections/orderings through a missing navigation yield null rather than dropping rows — with the explicit proviso that the decision be revisited later. This issue is that tracker. It is deliberately unscheduled; do not dispatch it as work.

What was decided and why (snapshot for the future reader)

• Implemented via the W6-1 PR (Complete GraphQueryModel semantics required for planner parity #210 group), which pins the semantics with translation snapshots, the contract tests NavigationEquality_NullMatchesMissingComplexProperty and NavigationProjection_MissingComplexPropertyYieldsNull, and a "null semantics of complex-property navigation" subsection in docs/core-concepts.md.
• Rationale at decision time: the strict-MATCH alternative silently dropped rows from OR-predicates/projections/orderings (the bug fixed in the PR-213 review); LINQ-to-objects parity is unachievable (p.Address.City on a null Address throws NRE in memory); strictness remains expressible opt-in (p.Address != null && p.Address.City == null).

When to reopen the question

Signals that should trigger the revisit: user confusion reports about == null matching missing navigations; a future explicit-existence operator (e.g. a Has()/Exists() surface in #96's operator track) making stricter defaults ergonomic; dialect divergence (#85/#86) where a provider can't honor null-propagation cheaply; or the in-memory provider (#112) surfacing a semantics mismatch between LINQ-to-objects and the graph translation that this decision papers over.

If/when revisited

Any change is breaking for query results — it needs a migration entry, updated pins (the named tests above are the contract), and a fresh decision comment from @savasp superseding the #221 record.

[savasp-agent]

Retained as a permanent exception to the zero-open-issues goal (@savasp, 2026-07-13). This deferred tracker stays open by design — do not close as part of reaching zero. Recorded in #113.

[savasp-agent]

@savasp reconfirmed on 2026-07-15 under the revised exit criterion: this issue remains open and is explicitly deferred. It does not block program exit. Do not dispatch without a future @savasp scheduling decision.