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Evidencechalk-194

Interpolated template expressions that evaluate to `undefined` or `null` throw exception

chalk#194, at commit 106f086. A closed issue from a repository Credda did not choose.

LIVE2026-09-20

RIGHT_FAILURE

executed against the upstream checkout.

Outcome
PATCH_REJECTED
Wall time
110.0s
Checks
5 passed of 5 applicable

RECORDED

NOT_GRADED

graded from the transcript committed with this case.

Outcome
not recorded
Checks
none run
Repository
chalk/chalk
Issue
#194
Pinned commit
106f086aaf00467b7161f8cec4b6cd255c30169f

01The signal

The report, exactly as it was filed.

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

chalk#194 · as filedcommit 106f086

Interpolated template expressions that evaluate to `undefined` or `null` throw exception

Getting the following error message with template literals:

```
> chalk`hello ${undefined}`

TypeError: Cannot read property 'toString' of undefined
    at chalkTag (/src/bitlang/bootstrap/node_modules/chalk/index.js:210:25)
    at Chalk.chalk.template (/src/bitlang/bootstrap/node_modules/chalk/index.js:36:20)
```
Repository
chalk/chalk
Issue
#194
Commit
106f086aaf00467b7161f8cec4b6cd255c30169f
Why this commit
The fix commit's parent where the closing commit was identifiable in the repository, otherwise the commit that was HEAD of the default branch at the moment the issue was filed.
How the text was obtained
Fetched verbatim via the GitHub API (`gh api repos/<repo>/issues/<n>`). Title on the first line, body unmodified below it. Nothing was paraphrased, cleaned up, or supplemented.
Toolchain
javascript · node · ava · npm

02What counts as reproducing it

The bar, written down before the run.

expected.reportedFailurecommitted with the case
Symptom
Tagging a template literal whose interpolated expression evaluates to undefined or null throws TypeError: Cannot read property 'toString' of undefined out of chalkTag, instead of rendering the value.
Where that came from
The only code block in the body: the REPL line ``> chalk`hello ${undefined}` `` followed by `TypeError: Cannot read property 'toString' of undefined` and a stack trace whose first frame is `at chalkTag (/src/bitlang/bootstrap/node_modules/chalk/index.js:210:25)`. The opening sentence -- "Getting the following error message with template literals:" -- says this was pasted from a run.

03What happened

The live run reproduced the reported failure.

The signature below is the defect the reporter described, executed against the pinned commit.

captured failure signatureLIVE · normalized
TypeError: Cannot read properties of undefined (reading 'toString')
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-capturedpassTypeError: Cannot read properties of undefined (reading 'toString')
right-failurepassReproduced the reported failure: Tagging a template literal whose interpolated expression evaluates to undefined or null throws TypeError: Cannot read property 'toString' of undefined out of chalkTag, instead of rendering the value.
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 106f086, 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/chalk/chalk
git checkout 106f086aaf00467b7161f8cec4b6cd255c30169f
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