There is a null class/type whose one and only instance is the special object nil.
This nil also itself names a type which contains no instance: its domain of values is the empty set. This is the type at the bottom of the type spindle, corresponding to the NULL that you're talking about.
nil is a special self-evaluating symbol representing Boolean false, the empty list, and this bottom type.
So you see, if we just don't conflate the null object with the null set type, everything works out.
There is a null class/type whose one and only instance is the special object nil.
This nil also itself names a type which contains no instance: its domain of values is the empty set. This is the type at the bottom of the type spindle, corresponding to the NULL that you're talking about.
nil is a special self-evaluating symbol representing Boolean false, the empty list, and this bottom type.
So you see, if we just don't conflate the null object with the null set type, everything works out.