Some blogs recently pondered on the Samurai Principle. It made me think, because I'm one of the many "guilty" of returning None/null rather than raising an exception. To me, it happens more often when working with Python rather than Java, because it's very natural to write "if something_not_found: return None". Also, abusing exceptions can end up polluting your code with dozens of nested try-catch/except, which kill readability and tend to be much worse than a simple "if (obj is None):".
This said, I agree that NullPointerExceptions are a royal pain, and "AttributeError: 'NoneType' object has no attribute 'something' " is equally bad to deal with. API programmers in particular should try hard to return this sort of stuff as little as possible.
I guess the bottom line is that in medium stat virtus, as it's often the case with these "absolute principles of programming"; at the end of the day, when we program we are applying science, not demonstrating it. And as much as we love them, samurai lost all their wars ;)