Role problem in Windows

Hi,
Running 9.1 on Windows 10, upgrading to 10 with pg_upgrade.

"Once upon a time" there was a bug in our automatic role creation 
procedure that did not mask vowels with accent (used in Italian 
language), like "ò, è" and the result was a role with an empty name.
We are now upgrading to 10, and pg_dumpall exits complaining with this 
role, showing its name (with mis-encoded UTF-8 accented vowel) as an 
invalid utf-8 character.

Trying to get rid of the role, that can't be deleted with a drop role 
because of the empty name, I did
delete from pg_authid where oid = nnnn

Role disappeared from role list.

At the next execution of the pg_upgrade it complains that role "nnnn" 
does not exist while dumping a trigger function. I tried remove the 
privilege from function ACL, but "role nnnnn does not exists".

Is there a way to recreate the deleted role, either as a dummy, so I can 
finish upgrade?
Is there another way to bypass the problem?

Any help would be appreciated.

Cheers,
Moreno.-