The documentation clearly states that interfaces which return null or throw an exception are behaving as expected.
Therefore such interfaces don't break the LSP, since they behave as expected. If the documentation said "interfaces never return null" then an interface returning null would violate the LSP. Since the documentation says the exact opposite, returning null is fine.
I think you need to get used to the fact that the LSP is intended to provide developers with something useful. We want different behaviour while having contracts fulfilled. I have the impression you would go to a DIY store and complain that they have paints in different colours, because paints in different colours violate the LSP. No, they don't. Do I complain to my user interface designer that replacing a green button with a blue button violates the LSP? No, I don't. They look different, but they can be substituted for each other. If the LSP didn't allow this, then frankly nobody would know what the letters mean and there would be no Wikipedia entry, because it would be useless.