Oracle数据库 nlssort函数中排序参数为空时，会按照什么规则进行排序？

Oracle 数据库执行如下用例：
drop table qz_people;
create table qz_people (id int, name varchar2(30));

insert into qz_people values (42, ‘Arthur Dent’);
insert into qz_people values (44, ‘Tricia mcmillan’);
insert into qz_people values (43, ‘Ford prefect’);
insert into qz_people values (45, ‘Zaphod Beeblebrox’);
查询结果如下：
select name from qz_people order by nlssort(name, null);