How to determine if NULL is contained in an array in Postgres?

Question

How do I determine if NULL is contained in an array in Postgres? Currently using Postgres 9.3.3.

If I test with the following select it returns contains_null =

Answer 1

select exists (
    select 1 
    from unnest(array[1, null]) s(a)
    where a is null
);
 exists 
--------
 t

Or shorter:

select bool_or(a is null)
from unnest(array[1, null]) s(a)
;
 bool_or 
---------
 t