NULL Type

12-1
The NULL type is used where data in a component either must be null (that is, empty), or not accessible.

External Form -- Input

The only valid input is a null value.

External Form -- Output

A null value is always returned.

Local Form and Behavior

The component can be created by an input operation, but no contents are modified. If it already exists, no data is modified.

Named Values

Named values are not applicable to the NULL type.

Constraints

Constraints are not applicable to the NULL type.