presto-main/src/main/java/io/prestosql/sql/planner/iterative/rule/CanonicalizeExpressionRewriter.java/CanonicalizeExpressionRewriter/rewriteIsNotNullPredicate
class CanonicalizeExpressionRewriter:        @Override
        public Expression rewriteIsNotNullPredicate(IsNotNullPredicate node, Void context, ExpressionTreeRewriter<Void> treeRewriter)
        {
            Expression value = treeRewriter.rewrite(node.getValue(), context);
            return new NotExpression(new IsNullPredicate(value));
        }