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: In JavaScript, typeof null evaluates to 'object'. Checking only typeof profile === 'object' allows null through, causing a null pointer error when reading properties.
The fix: Explicitly check that profile is not null: typeof profile === 'object' && profile !== null
Remember: In JavaScript, typeof null === 'object' is a historical quirk that requires an explicit null check.
The pattern behind it: null and undefined errors.
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