The NULLIFY statement causes pointers to become disassociated.
A pointer_object must be definable and have the POINTER attribute.
A pointer_object must not depend on the value, bounds, or association status of another pointer_object in the same NULLIFY statement.
Always initialize a pointer with the NULLIFY statement, pointer
assignment,
default initialization
or explicit initialization.
TYPE T INTEGER CELL TYPE(T), POINTER :: NEXT ENDTYPE T TYPE(T) HEAD, TAIL TARGET :: TAIL HEAD%NEXT => TAIL NULLIFY (TAIL%NEXT) END