Data type for representing untyped null (None) values. A null type has no
other value except null (None), thus, it can be cast to any nullable type.
This type helps in representing unknown types in API calls that use a null
(None) literal as well as bridging to formats such as JSON or Avro that
define such a type as well.
The null type is an extension to the SQL standard.
NullType is still not supported yet.