Thinking more about this, null object are meant to be neutral with respect to some behaviour, but that behaviour isn't really specified alongside the object. It

Thinking more about this, null object are meant to be neutral with respect to some behaviour, but that behaviour isn't really specified alongside the object. It seems like it's a weaker reinvention of the idea of an "identity element" from e.g., the `Monoid` typeclass. I say "weaker" because `Monoid` specifies the neutral element (`mempty`) alongside the behaviour (`mappend`), whereas the null object pattern does not.