Null is - together with scala.Nothing - at the bottom of the Scala type hierarchy.
Null is the type of the
null literal. It is a subtype of every type
except those of value classes. Value classes are subclasses of AnyVal, which includes
primitive types such as Int, Boolean, and user-defined value classes.
Null is not a subtype of value types,
null is not a member of any such type.
For instance, it is not possible to assign
null to a variable of type scala.Int.