I have been assisting several groups in doing similar migrations and would
be interested in any all feedback or notes on your efforts so we can
publish them on the wiki to assist the entire community.
On this specific issue I am not sure I understand the functionality you
are seeing in OpenJPA. During detachment (through serialization) if a null
reference or empty collection is returned I am unsure how the application
would differentiate this state from the scenario where the entity actually
had a null or empty collection. We have always sided with throwing an
exception versus returning an entity in a state which may be incorrect.
Can you provide more insight as to how your application differentiates a
null value or empty collection caused by serialization versus one that is
actually null or empty?