I found a group example in jbpm-examples. I found that the creator and actualowner is also null. I think that's by design since the user not yet pick up the task yet. I found that JBPM 5 is using hibernate 3.3. I will try to downgrade the hibernate version and see how's the SQL are generated. I guess the implicit join in the query t.taskData.createdBy and t.taskData.actualOwner force the hibernate engine to generate inner join statement.