Null is perfectly fine in place of an object. The author mentions this saves you debugging time. No, it will cause you pain later because you won't see errors that should happen. Instead they are masked by operating on some dummy object that you don't give a rats ass about.
For modules I write in C, I only have one function that can return NULL---the function that creates a new structure. All other functions that work with that structure assume (backed by an assert()) that the passed in pointer will not be NULL. For the code I write, there is no reason for functions to accept a NULL pointer. And it's less painful that it sounds. I got the idea from _Writing Solid Code_, one of only two books that fundamentally changed how I write code (the other being _Thinking Forth_).
The right way to work around null for scalar variables is to use Maybe/Option, preferably in a language with pattern matching, as opposed to using "magic values" like 0 or the empty string. This means removing null pointer errors by construction.