ResultSet got NullPointerException on getMetaData calls

Hello to all,
I got a NullPointerException when try to call getMetaData method on a refcursor
mapped on a ResultSet.
This is an example scenario:

create table mytable(name varchar, surname varchar, email varchar);
create or replace function myfunction() returns refcursor as'
declare
rc refcursor;
begin
open rc for select * from mytable order by surname;
return rc;
end;

This is a piece of code using the above stored function:

conn.setAutoCommit(false);
CallableStatement proc = conn.prepareCall("{ ? = call myfunction() }");
proc.registerOutParameter(1, Types.OTHER);
proc.execute();
ResultSet rs = (ResultSet) proc.getObject(1);
ResultSetMetaData rsmd = rs.getMetaData(); // <- NullPointerException

I'm using the PostgreSQL 7.4 server and the PostgreSQL JDBC 7.4 drivers.
Reading a previous post by Tomas on this ML I've tried to use the PostgreSQL
JDBC 8.0 driver without succes, the exception stills here.

Thank you for support,
Gaetano Sferra

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