Correlated subquery producing wrong schema

create table test(id int, name string,dept string);
insert into test values(1,'a','it'),(2,'b','eee'),(NULL, 'c', 'cse');
select distinct 'empno' as eid, a.id from test a where NOT EXISTS (select c.id from test c where a.id=c.id);

+-------+--------+
|  eid  |  a.id  |
+-------+--------+
| NULL  | empno  |
+-------+--------+