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Grouping metadata mistakes real null keys for omitted dimensions · case 05

Grouping metadata mistakes real null keys for omitted dimensions.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

Expand every fact [a,b,payload] once per supplied grouping-set list of column positions. Emit [projected-a,projected-b,grouping-mask,payload], using None for omitted keys and bit 1 for omitted a, bit 2 for omitted b. Preserve duplicate grouping sets and null source keys.

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
real null key	`[[null, "b", 1, 5]]`	`[[null, "b", 0, 5]]`	Failed

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