Flush Hibernate issue

Guys,
I am facing the following exception. I am using Hibernate 3.2.3 and Oracle 9.2.1 driver. I also face a nullpointerexception at org.hibernate.type.PrimitiveType.toString(PrimitiveType.java:15) during session flush. What could be the possible reasons?
Any help would be highly appreciated.

java.lang.NullPointerException
at oracle.jdbc.dbaccess.DBData.clearItem(DBData.java:431)
at oracle.jdbc.dbaccess.DBDataSetImpl.clearItem(DBDataSetImpl.java:3528)
at oracle.jdbc.driver.OraclePreparedStatement.checkBindTypes(OraclePreparedStatement.java:3271)
at oracle.jdbc.driver.OraclePreparedStatement.setNull(OraclePreparedStatement.java:1322)
at org.hibernate.type.NullableType.nullSafeSet(NullableType.java:129)
at org.hibernate.type.NullableType.nullSafeSet(NullableType.java:107)
at org.hibernate.persister.entity.AbstractEntityPersister.dehydrate(AbstractEntityPersister.java:1997)
at org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:2371)
at org.hibernate.persister.entity.AbstractEntityPersister.updateOrInsert(AbstractEntityPersister.java:2307)
at org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:2607)
at org.hibernate.action.EntityUpdateAction.execute(EntityUpdateAction.java:92)
at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:248)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:232)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:140)
at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:298)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1000)

Have you assigned this property a value or is it null?

Paul,
The problem is there is so much of activity on the session, that it is too difficult to trace why this is occurring. The NPE is not helpful in understanding the issue. Can you quote some examples as to why this could occur? Or have you faced something similar to this?

Somewhere you have used a primitive type for an object property. This property is probably maps a nullable field? Primitives can't be null. Check your mappings; make sure where you are using a primitive type you are not using it for a nullable field.

Paul,
Thanks for your input... But by primitype mapping for example do you mean a char or Character. If its a char am not using that. But if you are also taking about the wrappers, I will double check my code.
You have been wonderful replying so quickly buddy.. Thanks again. But I am gonna bug you until I understand/ am able resolve the issue.

But by primitype mapping for example do you mean a char or Character

char, int, byte, short, long, double etc.

You have been wonderful replying so quickly buddy.. Thanks again. But I am gonna bug you until I understand/ am able resolve the issue.

No bother. Keep pestering

Does that mean, if I have a char in my class and use character in my hbm, It could be where the issue is?

If you have a primitive that represents a field that can be null, you should be using the wrapper type instead (so yes, Character rather than char).

Hey thanks buddy... I found the issue with your help. Like you said a Character was being set to null, but the question is how come it does not throw the error whenever the field is null?