nextval per counted

I'm trying to craft SQL to invoke a sequence nextval once per grouped value.

So far I have this:

with husb as(
select e.ma, count(distinct coalesce(e.pa, nextval('egogen')::text)) as mates
from emp_all_by3 e group by e.ma order by mates
)
select mates, count(*)
from husb
group by mates order by mates desc;

which works nicely but it "ids" each null separately.

The following lets me count the "fixes" as a mate

with husb as(
  select e.ma, count(distinct coalesce(e.pa, nextval('egogen')::text)) mates
  from emp_all_by3 e
  where ma is not null
  group by e.ma order by mates
)
select mates, count(*) from husb group by mates order by mates desc;

with husb as(
  select e.ma, coalesce(e.pa,'fix') as pa
  from emp_all_by3 e
  where e.ma is not null
),
fixed as (
  select e.ma, count(distinct e.pa) mates
  from husb e group by e.ma order by mates
)
select mates, count(*) from fixed group by mates order by mates desc;

but I would love to able to assign a single "nextval"  to those fixes.

Any pointers appreciated.