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: dict.get(key, default) only uses the default if key is absent from the dictionary. If key exists with value None, None is returned.
The fix: Explicitly check if the retrieved value is None: default_val if val is None else val
Remember: In Python, dict.get() returns the stored value (even None) if the key exists.
The pattern behind it: null and undefined errors.
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