dbName == null should be interpreted as default database

If the name of a database is null, it should be hendled exactly as if the name of the database was set to the default database's name

Background: In the Torque 4 trunk, the setDbName in the generated peers is generated as follows:
private static void setDbName(Criteria crit) throws TorqueException
{
if (!Torque.isInit())

{ throw new TorqueException("Torque is not initialized"); }

if (Torque.getDefaultDB().equals(crit.getDbName()))
{
crit.setDbName(${peerClassName}.DATABASE_NAME);
}
}
So if I set the database name to the name of the default db it is always switched to the name of the table's default when querying the database, which I did not mean to do.
In Torque 3 the check was == instead of equals, which did the trick but caused findbugs to yell.
The clean solution is to use null for "not set" in the criteria.