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: the user has no address, so user.address is undefined. Reading .city from undefined crashes.
The fix: return user.address?.city ?? "Unknown";
Remember: before reading a value inside another value, check that the outer one exists.
The pattern behind it: null and undefined errors.
Paste this into any web page or blog post. Visitors fix the bug right there, in their browser.
<iframe src="https://trybughunt.com/embed/28bd9e12-d686-4f84-bb89-0bfc6effb9df" title="Debugging challenge: Dashboard crashes for a user with no address" 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/28bd9e12-d686-4f84-bb89-0bfc6effb9df">TryBugHunt</a></p>