TypeError: Cannot destructure property 'rule' from null or undefined value

## Error

```
Cannot destructure property 'rule' from null or undefined value
```

## Stack trace

```
[native code] in forEach
```

## Tracking Details
- **Project**: exercism-js
- **Sentry**: [TypeError: Cannot destructure property 'rule' from null or undefined value](https://thalamus-ai.sentry.io/issues/140801366/)
- **Culprit**: forEach([native code])
- **First seen:** Aug 15, 2026

Start with the linked Sentry event and its stack trace, then trace the exercism-js code path containing the native forEach call. Confirm which value is null or undefined and document a reproducible case; done means the TypeError no longer occurs and the relevant behavior is covered by a regression test.

Written by the indexing model from the issue text.