Time: 0:00
Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).
This bug belongs to the null and undefined errors pattern
Cannot read properties of undefined, NoneType has no attribute, NaN appearing from nowhere.
What went wrong: user?.address gives undefined for {}, and then .city is read from undefined. Only the first step was protected.
The fix: return user?.address?.city ?? "unknown";
Remember: put ?. on every step that might be missing.
The pattern behind it: null and undefined errors.
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<iframe src="https://trybughunt.com/embed/f77b19ef-5068-4b49-a0e1-207a9d4b9158" title="Debugging challenge: City lookup still crashes with ?." 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/f77b19ef-5068-4b49-a0e1-207a9d4b9158">TryBugHunt</a></p>