presto-main/src/main/java/io/prestosql/sql/relational/SqlToRowExpressionTranslator.java/SqlToRowExpressionTranslator/visitIsNotNullPredicate
class SqlToRowExpressionTranslator:        @Override
        protected RowExpression visitIsNotNullPredicate(IsNotNullPredicate node, Void context)
        {
            RowExpression expression = process(node.getValue(), context);

            return notExpression(new SpecialForm(IS_NULL, BOOLEAN, ImmutableList.of(expression)));
        }