Null objects exist. They make perfect sense on their own. They are an appropriate thing to return when you want to fail to produce a useful object, but do it silently in a chained set of method calls. Just return a Null and let the caller deal with it.

Think of NULL in a database. It represents missing data. It can appear when you expected any other data type. There aren't (well, except in some vendor extensions) different kinds of NULLs. There don't have to be.

What are your alternatives? What could have been a simple chain of method calls followed by one if now has to turn into a nested set of if's as you test every method call for success to know if you can make the next. Or you have to wrap it in an eval and complicate your error handling needlessly. The Null is clean, simple, understandable, and that is all that is needed to justify Null's existence.