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Dependent defaults treat an explicit null source as zero · case 05

Dependent defaults treat an explicit null source as zero.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

Materialize missing columns using ordered default rules [target,source-or-None,constant]. A constant rule writes constant; a dependent rule writes source+constant, propagating explicit null. Existing columns including None and zero never change. Resolve forward dependencies to a fixed point; unresolved dependencies return DEFAULT_CYCLE.

Why this case matters

A bounded deterministic data engine model makes representation and changelog faults reproducible.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
explicit null	`{"a": null, "b": 1}`	`{"a": null, "b": null}`	Failed

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