Time: 0:00
This is a null and undefined errors bug
Cannot read properties of undefined, NoneType has no attribute, NaN appearing from nowhere.
An arrow function only returns its expression automatically when there are no curly braces: (price) => price + 5. Add braces and it becomes a normal function body, which needs an explicit return; without one, every call returns undefined. map() faithfully collects those undefineds, which is why the length is right and the values are not. Either drop the braces or write return. The giveaway for this bug is always an array of undefined the same length as the input.
The pattern behind it: null and undefined errors.
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<iframe src="https://trybughunt.com/embed/53eedadc-6f92-459c-8d13-5c1ae37d3980" title="Debugging challenge: Price list full of undefined" width="100%" height="580" loading="lazy" style="border:1px solid #d4d4d8;border-radius:12px;max-width:760px"></iframe>
<p style="font-size:14px">Debugging challenge from <a href="https://trybughunt.com/challenges/53eedadc-6f92-459c-8d13-5c1ae37d3980">BugHunt</a></p>