Serialize Exception

OK here is code :

Ziu z = new Ziu();

Class.forName("org.postgresql.Driver");
db = DriverManager.getConnection(url, usr, pwd);

Serialize.create((org.postgresql.Connection) db,z.getClass());

Serialize s = new Serialize((org.postgresql.Connection) db,
Serialize.toPostgreSQL( z.getClass().getName() ) ) ;
//and here i have Exception described below

int oid = s.store(z);

Ziu zz = (Ziu ) s.fetch(oid);

============================

Exception in thread "main" java.lang.NullPointerException
at org.postgresql.jdbc2.ResultSet.getString(ResultSet.java:148)
at org.postgresql.util.Serialize.create(Serialize.java:241)
at Test.main(Test.java:31)

============================

Please I need help with that !!!!
Why is the Exception , what should I do to avoid that (...) Exception!

--
MS is not the answer.
MS is the question.
NO (or Linux) is the answer.

:) Jarek (:

-------------------------------------------------------

--
MS is not the answer.
MS is the question.
NO (or Linux) is the answer.

:) Jarek (: