This case was supposed to be covered by the last bullet point, "instances of user-defined classes, if the class defines a __bool__() or __len__() method, when that method returns the integer zero or bool value False.".  The word "user-defined" should be dropped.

Also, the whole section can be simplified to something like:

"""
By default, objects are considered true unless they define either a __bool__ method that returns False or __len__ method that returns zero.  

Practically, this means that empty containers are false (such as [], (), {}, '', etc) and that numbers equal to zero are false (such as 0, 0.0, 0.0j, False, Decimal(0), Fractions(0, 1), etc).  Also, *None* is a false value.


"""