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: config[key] crashes with KeyError when the key is missing.
The fix: return config.get(key, "default")
Remember: use .get(key, fallback) when a key might not be there.
The pattern behind it: null and undefined errors.
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