Function x returns opaque in error typeidTypeRelid

Hello,

I am a bit at a loss here.
If I create a function  which returns something it works fine.
If it returns opaque I get the following: ERROR:  typeidTypeRelid: Invalid
type - oid = 0
What am I doing wrong ?

Thanks in advance.
Best regards,
Roelof Sondaar

dhcp=# drop function lalala();
DROP
dhcp=# create function lalala() returns opaque as '
dhcp'# declare
dhcp'#     sname       text;
dhcp'# begin
dhcp'#     sname:= ''lalala'';
dhcp'# end;
dhcp'# ' language 'plpgsql';
CREATE
dhcp=#
dhcp=# select lalala();
ERROR:  typeidTypeRelid: Invalid type - oid = 0
dhcp=#
dhcp=# drop function lalala2();
DROP
dhcp=# create function lalala2() returns text as '
dhcp'# declare
dhcp'#     sname       text;
dhcp'# begin
dhcp'#     sname:= ''lalala'';
dhcp'#     return sname;
dhcp'# end;
dhcp'# ' language 'plpgsql';
CREATE
dhcp=#
dhcp=# select lalala2();lalala2
---------lalala
(1 row)