presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/visitNullPredicate
class AstBuilder:    @Override
    public Node visitNullPredicate(SqlBaseParser.NullPredicateContext context)
    {
        Expression child = (Expression) visit(context.value);

        if (context.NOT() == null) {
            return new IsNullPredicate(getLocation(context), child);
        }

        return new IsNotNullPredicate(getLocation(context), child);
    }