CREATE OR REPLACE PACKAGE PKG IS

  SUBTYPE BOOLEAN_NOT_NULL IS BOOLEAN NOT NULL;

  PROCEDURE ASSERT(CONDITION_IN IN BOOLEAN);

  PROCEDURE ASSERT_NN(CONDITION_IN IN PKG.BOOLEAN_NOT_NULL);

END PKG;

CREATE OR REPLACE PACKAGE BODY PKG IS

  PROCEDURE ASSERT(CONDITION_IN IN BOOLEAN) IS
  BEGIN
    IF CONDITION_IN THEN
      RETURN;
    ELSIF NOT CONDITION_IN THEN
      RAISE_APPLICATION_ERROR(-20001, 'FAILED');
    ELSE
      RAISE_APPLICATION_ERROR(-20002, 'UNKNOWN');
    END IF;
  END ASSERT;

  PROCEDURE ASSERT_NN(CONDITION_IN IN PKG.BOOLEAN_NOT_NULL) IS
  BEGIN
    IF CONDITION_IN THEN
      RETURN;
    ELSIF NOT CONDITION_IN THEN
      RAISE_APPLICATION_ERROR(-20001, 'FAILED');
    ELSE
      RAISE_APPLICATION_ERROR(-20002, 'UNKNOWN');
    END IF;
  END ASSERT_NN;

END PKG;

EXEC PKG.ASSERT(1=1);
EXEC PKG.ASSERT(1=2);
EXEC PKG.ASSERT(NULL IS NULL);
EXEC PKG.ASSERT(NULL=1);
EXEC PKG.ASSERT(NULL);

EXEC PKG.ASSERT_NN(1=1);
EXEC PKG.ASSERT_NN(1=2);
EXEC PKG.ASSERT_NN(NULL IS NULL);
EXEC PKG.ASSERT_NN(NULL=1);
EXEC PKG.ASSERT_NN(NULL);

PL/SQL procedure successfully completed.
ORA-20001: FAILED
PL/SQL procedure successfully completed.
ORA-20002: UNKNOWN
ORA-20002: UNKNOWN


PL/SQL procedure successfully completed.
ORA-20001: FAILED
PL/SQL procedure successfully completed.
ORA-06502: PL/SQL: numeric or value error
PLS-00567: cannot pass NULL to a NOT NULL constrained formal parameter