FA-4026 / Serialization / Open access

An empty query field is confused with an absent field · case 01

An empty query field is confused with an absent field.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The implementation applies an operation whose text or grammar semantics violate this contract: Return all values of key a from a form query, retaining empty and repeated values.

VERIFIED REPAIR

Implement the complete stated contract, including the boundary fixtures: Return all values of key a from a form query, retaining empty and repeated values.

Unsuccessful approach: The attempted repair handles the primary example but still violates a separate boundary of the same contract.

Case contract

Return all values of key a from a form query, retaining empty and repeated values.

Why this case matters

A local executable model for consumers of structured text; oracle values are authored literals, not outputs copied from the repaired implementation.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return [v for k,v in parse_qsl(x) if k=='a']
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('a='), [''])
check('boundary 2', solve('b=1'), [])
check('boundary 3', solve('a=1&a=2'), ['1', '2'])
check('boundary 4', solve(''), [])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary 1	`[]`	`['']`	Failed
boundary 2	`[]`	`[]`	Passed
boundary 3	`['1', '2']`	`['1', '2']`	Passed
boundary 4	`[]`	`[]`	Passed

SHA-256 / f23f467672598de3074008b7cb1e24e2cfe09483ec0425c52e15b04a4deab356

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return [dict(parse_qsl(x,keep_blank_values=True)).get('a','')]
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('a='), [''])
check('boundary 2', solve('b=1'), [])
check('boundary 3', solve('a=1&a=2'), ['1', '2'])
check('boundary 4', solve(''), [])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary 1	`['']`	`['']`	Passed
boundary 2	`['']`	`[]`	Failed
boundary 3	`['2']`	`['1', '2']`	Failed
boundary 4	`['']`	`[]`	Failed

SHA-256 / ea003b385240408f611809543e91c9860e5e31c4f98ef3a6cb118d917ff4bcc6

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return [v for k,v in parse_qsl(x,keep_blank_values=True) if k=='a']
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('a='), [''])
check('boundary 2', solve('b=1'), [])
check('boundary 3', solve('a=1&a=2'), ['1', '2'])
check('boundary 4', solve(''), [])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary 1	`['']`	`['']`	Passed
boundary 2	`[]`	`[]`	Passed
boundary 3	`['1', '2']`	`['1', '2']`	Passed
boundary 4	`[]`	`[]`	Passed

SHA-256 / 07d7a120e8ab5fe85d75bc684b7d8bcc9cfaa8c22f6ac55502a585b10b0c2c4a

Verification & scope

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.

Observations recorded using Python 3.12.14 at 2026-09-29T14:37:34.615898+00:00.

Case digest / bc778db3a97f9308a1f2aa59ec5fabaf2299b568248b01437eeb4001a739e030