NotNull

An instance of NotNull[A] indicates that A does not have a static type of Null.

This can be useful in preventing Null from being inferred when a type parameter is omitted.

This trait is used along with ambiguous implicits to achieve the goal of preventing inference of Null. This ambiguous implicit trick has been used in the Scala community for some time. Here is an early example of such a trick being used in a similar way to prevent a Nothing type.