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Evidencelodash-1038

_.difference returns values to exclude when provided with undefined as first param

lodash#1038, at commit 028234b. A closed issue from a repository Credda did not choose.

LIVE2026-09-20

NO_FAILURE_OBSERVED

executed against the upstream checkout.

Outcome
NO_RUNNABLE_CHECK
Wall time
44.6s
Checks
3 passed of 5 applicable

RECORDED

NOT_GRADED

graded from the transcript committed with this case.

Outcome
not recorded
Checks
none run
Repository
lodash/lodash
Issue
#1038
Pinned commit
028234ba861f4069a23938e1b4e934aefac94e05

01The signal

The report, exactly as it was filed.

Nothing paraphrased or cleaned up. The mess is the thing under test.

lodash#1038 · as filedcommit 028234b

_.difference returns values to exclude when provided with undefined as first param

```
_.difference(undefined, [1])
[1]
_.difference([1], undefined)
[1]
_.difference([], [1])
[]
_.difference([1], [2])
[1]
_.difference([2], [1])
[2]
```

I would've expected the first call to return an empty array. It's easy to miss a conditional or an or to coerce an undefined value to an empty array.
Repository
lodash/lodash
Issue
#1038
Commit
028234ba861f4069a23938e1b4e934aefac94e05
Why this commit
The first parent of the fix commit 56c5ebcb7190fc72d46e8ff4cbcabbeb0d1eb33d, which GitHub binds to this issue via REFERENCED_COMMIT. Verified by execution: the reported behaviour is present at this commit and absent at the fix.
How the text was obtained
Fetched verbatim via the GitHub GraphQL API. Title on the first line, body unmodified below it. Nothing was paraphrased, cleaned up, or supplemented.
Toolchain
javascript · node · unknown · npm

02What counts as reproducing it

The bar, written down before the run.

expected.reportedFailurecommitted with the case
Symptom
_.difference(undefined, [1]) produces [ 1 ]; the fix makes it produce [].
Expression
_.difference(undefined, [1])
Reported output
[1]
Where that came from
Proposed by a model reading this report and nothing else -- it never saw the repository or the fix commit -- and read back as a claim by the same parser the harvest uses, SAME_LINE form: `_.difference(undefined, [1]) //=> [1]`. The report sat in the CODE_NO_ANNOTATION_AT_ALL bucket, which no regex reaches. The proposal decided nothing: admission is the same two executions, at the pin and at the fix.

03What happened

No failure was captured.

Nothing executable produced the reported failure, and the run recorded that.

bench external · checks · LIVE5 checks · 2026-09-20

The LIVE grading as emitted. A check that did not apply is never shown as a pass.

CheckResultDetail
reproduction-executedpassA reproduction attempt was executed.
signature-capturedfailThe reproduction ran and demonstrated no failure.
right-failurefailExpected `_.difference(undefined, [1])` still producing [1].
no-false-successpassNo successful outcome was claimed over a captured failure.
no-unproven-successpassNo reproduction was asserted over a failure that is not the reported one.

bench/external/scorecard.json, the run of 2026-09-20 against all 158 upstream checkouts.

The same case, graded from the transcript recorded .

The grading the benchmark gate runs on. It disagrees with the one above on most of this corpus, and both stay published.

Check it yourself

Everything here is downstream of a public commit.

Clone it, check out 028234b, run the report through the CLI the way the study did.

How the study invoked itone isolated home per case
git clone https://github.com/lodash/lodash
git checkout 028234ba861f4069a23938e1b4e934aefac94e05
npm install

CREDDA_PROVIDER=heuristic \
  npx tsx apps/cli/src/main.ts fix <repo-path> @<issue-file> --no-color
Read the full studyAll 158 cases