"Making everything a reference: The Billion Dollar Mistake" is the talk I want to see
I wish C had a feature that would let you allocate something on the stack and then return to the parent stack frame without popping the stack-pointer - that would be handy for self-contained object-constructors.
I think the difference comes from dynamic vs static typing. In Python, you sort of get into the habit of "defensive" programming: checking inputs to your function, catching Nones, etc.
In java, you tend to rely more on the type system. If it typechecks/compiles, there's a good chance it's OK. That is, until you get a null value that's not handled.
That's the root issue I think: If null is an acceptable value per the type, then the same type system should force you to handle it. As do the type systems in ML languages for option types, for example.
Nothing about this precludes the usage of sentinel values.
>>> a=[2, 3, 1]
>>> b=a
>>> id(a)
139731931982216
>>> id(b)
139731931982216
>>> b
[2, 3, 1]
>>> b.sort()
>>> del(b)
>>> a
[1, 2, 3]
>>>2, 3 and 1 have id's. That's what "everything is an object" fleshes out to in Python. But they don't reference other objects because they are literals. The value of 2 is also its name.
AttributeError: 'NoneType' object has no attribute 'foo'
Oh, I guess except for shadowing an outer-scope variable with a local that you never initialize. That just gives you the wrong answer in Python, because there exists no local without an initialization. But it's a pretty marginal case.