I have a daemon thread that is pulling email messages out of the database to retry sending if sending failed. I am running into the following exception that gets thrown repeatedly.

Note it is possible that this is a threading issue - it is possible that one thread is removing these objects from the database while another one is also manipulating them in the database. No idea if that has anything to do with it.

Any suggestions for a workaround appreciated.

java.lang.NullPointerException
        at com.db4o.internal.Platform4.hasWeakReferences(Unknown Source)
        at com.db4o.internal.ObjectReference.getObject(Unknown Source)
        at com.db4o.internal.PartialObjectContainer.objectForIDFromCache(Unknown Source)
        at com.db4o.internal.PartialObjectContainer.getActivatedObjectFromCache(Unknown Source)
        at com.db4o.internal.query.result.AbstractQueryResult.activatedObject(Unknown Source)
        at com.db4o.internal.query.result.IdListQueryResult.get(Unknown Source)
        at com.db4o.internal.query.result.StatefulQueryResult.get(Unknown Source)
        at com.db4o.internal.query.ObjectSetFacade.get(Unknown Source)
        at java.util.AbstractList$Itr.next(AbstractList.java:422)
        at java.util.AbstractCollection.toArray(AbstractCollection.java:176)
        at java.util.ArrayList.<init>(ArrayList.java:136)
        at org.netbeans.webapps.topicauction.mail.MailQueue$3.run(MailQueue.java:324)