| ERROR | subtype of a NOT NULL type must also be NOT NULL |
| CAUSE | After a subtype was defined as NOT NULL, it was used as the base type for another subtype defined as NULL. That is not allowed. For example, the code might look like DECLARE SUBTYPE Weekday IS INTEGER NOT NULL; SUBTYPE Weekend IS Weekday NULL; -- illegal instead of DECLARE SUBTYPE Weekday IS INTEGER NOT NULL; SUBTYPE Weekend IS Weekday; |
| ACTION | Revise the subtype definitions to eliminate the conflict. |