👉 A term that is often used in computer programming to describe a function or method that returns an undefined value if its argument is not provided. This can be useful for situations where you need to handle cases where it's impossible to determine the input, but your code still needs to work as expected. For example, in Python, you might use the `None` type to represent an undefined value: ```python def calculate_sum(a, b): if a is None or b is None: