PLS-01455: The predicates IS NULL and IS NOT NULL are defined only for column specifications
Cause: The predicates "IS NULL" and "IS NOT NULL" are defined only for column specifications, not for any other expressions. Section 5.15, "null_predicate", indicates that in the predicate "x IS NULL", x must be a column, and may not be any other kind of expression.
Action: Refer to ANSI document ANSI X3.135-1992 for details.