setObject on PGInterval throws "Unknown Type null"

We upgraded to JDBC Build 309 on PostgreSQL 8.0 from
JDBC Build 307 on PostgreSQL 7.4 and setObject now fails
on PGInterval

1)
if myPgInterval != null
Originally code: myPreparedStatement.setObject(i, myPGInterval)
It throws SQLException "Unknown type null"

We tried: myPreparedStatement.setObject(i, myPGInterval, Types.OTHER)
It throws "Unknown type null"

if myPgInterval == null
Original code: myPreparedStatement.setObject(i,myPGInterval)
It throws "setObject(i,null) is not supported. Instead, use setNull(i,type) or setObject(i,null,type)"

We tried: myPreparedStatement.setNull(i, Types.OTHER)
It throws "setNull(i, Types.OTHER) is not supported; use setObject(i,null, Types.OTHER) instead"

We tried: myPreparedStatement.setObject(i,myPGInterval,Types.OTHER)
It throws "setNull(i, Types.OTHER) is not supported; use setObject(i,null, Types.OTHER) instead"

How should setObject be coded with a PGInterval ?

2)
With JDBC Build 309, setObject requires an SQL Type when object == null,
this makes setObject(i, object) useless.

Why do JDBC requires an SQL Type when the same statement can be processed by psql
without the SQL type specified?

Why is a standard JDBC method setObject(i, object) rendered useless?
Is it supported by other DBMS?

Thanks
Jean-Pierre Pelletier