It's supposed to raise an AttributeError if the attribute is not present. The previous case was that magicmethods were not wrapped returning configured values. So this conflicts with the documentation returning a default value when not present instead of raising an AttributeError.

wraps: Item for the mock object to wrap. If wraps is not None then calling the Mock will pass the call through to the wrapped object (returning the real result). Attribute access on the mock will return a Mock object that wraps the corresponding attribute of the wrapped object (so attempting to access an attribute that doesn’t exist will raise an AttributeError).