BUG #11304: UNION query with NULL values fails

The following bug has been logged on the website:

Bug reference:      11304
Logged by:          Markus Woehling
Email address:      m.woehling@barthauer.de
PostgreSQL version: 9.3.5
Operating system:   Windows Server 2008
Description:

I want to "warm up" the bug reports "BUG #1453"
[http://permalink.gmane.org/gmane.comp.db.postgresql.bugs/7383] and "BUG
#5974"
[http://www.postgresql.org/message-id/201104122018.p3CKIlWR042915@wwwmaster.postgresql.org].

I need to build UNION queries with NULL values dynamically like in this
sample:
select null union all select null union all select 1;

This could be workaround:
select null union all (select null union all select 1);

But this workaround fails in this case:
select 1 union all (select null union all select null);

Because I don't know the "real" data type of the NULL values, I can't
specify the type like in this sample:
select 1 union all (select null::int union all select null::int);

I know that MSSQL, Oracle, MySQL, DB2 and Firebird don't have this problem.
So I'd really like to see this working in PostgreSQL as well.
Currently this problem hinders me from using PostgreSQL as DBMS in our
products.

Markus