{"abstract":"The operation returns a result or retained state that violates this contract: Look up a key and use the fallback only when absent; falsy present values are retained.","category":"Mapping semantics","checks":4,"contract":"Look up a key and use the fallback only when absent; falsy present values are retained. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","contract_signature":"x, y=None","evaluation_group":"model-a9feb8530f267e02","failed_approach":"Special-casing None still conflates a present None with a missing key.","family":"xr-map-get-preserves-falsy-value","id":"FA-4381","implementations":{"attempt":{"sha256":"18c4d67134b687b3142702989aaacbb1207ed5d1e7088057afa3dfeeb2303e4b","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return x.get(y[0],y[1]) if x.get(y[0]) is not None else y[1]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('zero value', solve({'a': 0}, ['a', 'fallback']), 0)\ncheck('None value', solve({'a': None}, ['a', 'fallback']), None)\ncheck('false value', solve({'a': False}, ['a', 'fallback']), False)\ncheck('missing key', solve({}, ['a', 'fallback']), 'fallback')\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"9f0e04dbaf77bd97466e29db451d800b57dbeb3602c772bbf439a6a0f12ee426","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return x.get(y[0]) or y[1]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('zero value', solve({'a': 0}, ['a', 'fallback']), 0)\ncheck('None value', solve({'a': None}, ['a', 'fallback']), None)\ncheck('false value', solve({'a': False}, ['a', 'fallback']), False)\ncheck('missing key', solve({}, ['a', 'fallback']), 'fallback')\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":" This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"xr-map-get-preserves-falsy-value","generated_at":"2026-09-29T14:37:38.509493+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A controlled local-runtime regression for collection APIs, language semantics, or ownership wrappers. Fixtures include boundary and interaction cases.","root_cause":"Boolean fallback treats present falsy values as absent.","sha256":"1d27697a9283fd9dd62405c65ebc1f3065d95db88ceb618ec6f4ebdca4b561f8","title":"Map get preserves falsy value · case 01","variant":1,"variant_policy":"Five execution reruns of a fixed adversarial fixture suite; variant number does not alter semantic inputs.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":36.94,"exit_code":1,"observations":[{"actual":0,"check":"zero value","expected":0,"passed":true},{"actual":"fallback","check":"None value","expected":null,"passed":false},{"actual":false,"check":"false value","expected":false,"passed":true},{"actual":"fallback","check":"missing key","expected":"fallback","passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"zero value\", \"actual\": 0, \"expected\": 0, \"passed\": true}, {\"check\": \"None value\", \"actual\": \"fallback\", \"expected\": null, \"passed\": false}, {\"check\": \"false value\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"missing key\", \"actual\": \"fallback\", \"expected\": \"fallback\", \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":36.349,"exit_code":1,"observations":[{"actual":"fallback","check":"zero value","expected":0,"passed":false},{"actual":"fallback","check":"None value","expected":null,"passed":false},{"actual":"fallback","check":"false value","expected":false,"passed":false},{"actual":"fallback","check":"missing key","expected":"fallback","passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"zero value\", \"actual\": \"fallback\", \"expected\": 0, \"passed\": false}, {\"check\": \"None value\", \"actual\": \"fallback\", \"expected\": null, \"passed\": false}, {\"check\": \"false value\", \"actual\": \"fallback\", \"expected\": false, \"passed\": false}, {\"check\": \"missing key\", \"actual\": \"fallback\", \"expected\": \"fallback\", \"passed\": true}], \"passed\": false}\n"}},"member_only":{"stages":["fixed"],"fields":["implementations.fixed","verification.fixed","harness","repair"],"note":"The verified repair, its recorded checks, the repair description, and the scoring harness are available to members."}}