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BreamoreBoy:
This is basically the definition of object.__format__:
def __format__(self, specifier):
 if len(specifier) == 0:
 return str(self)
 raise TypeError('non-empty format string passed to object.__format__')
Which is why it works for an empty specifier.
As a reminder, the point of raising this type error is described in the first message posted in this bug. This caused us an actual problem when we implemented complex.__format__, and I don't see object.__format__ changing.
Implementing NoneType.__format__ and having it understand some string specifiers would be possible, but I'm against it, for reasons I hope I've made clear.
As to why None.__format__ appears to be implemented, it's the same as this:
>>> class Foo: pass
... 
>>> Foo().__format__
<built-in method __format__ of Foo object at 0xb74e6a4c>
That's really object.__format__, bound to a Foo instance.