different results from plpgsql functions related to last changes in master

[Pavel Stehule]

Hi

I did update of plpgsql_check and I see, so some functions returns
different result than on older posgresql. Probably this is wanted behave,
but It should be mentioned as partial compatibility break, because some
regress test can be broken too.

create table t(i int);
create function test_t(OUT t) returns t AS $$
begin
    $1 := null;
end;
$$ language plpgsql;

select test_t();

result on PostgreSQL11 is null, on older is empty record "()"

Regards

Pavel