sum, min, max and null

Hi,

I understand that sum, min and max ignore null values. So for example
this query:

select sum(v),min(v) from (
select 1 as v
union all select null
union all select 3
) s

will result in sum(v)=4 , min(v)=1.

However, I'm in need of a different interpretation, where sum() should
change the output value to null if there is any NULL value in the input.
How do I achieve this? I was experimenting with this:

select case when sum(hasnull)>0 then null else sum(v) end as mysum from (
select v, case when v is null then 1 else 0 end as hasnull
from (
select 1 as v
union all select null
union all select 3
) s ) s2

It works but this is so ugly that I'm not even trying to use it in
production code. Is there any better way to do it?

Thanks,

Laszlo