Stateful beans should enlist the extended persistence context into the JTA independently of EntityManager invocation

"7.9.1 Container Responsibilities:

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For stateful session beans with extended persistence contexts:

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When a business method of the stateful session bean is invoked, if the stateful session bean uses container managed transaction demarcation, and the entity manager is not already associated with the current JTA transaction, the container associates the entity manager with the current JTA transaction and calls EntityManager.joinTransaction.
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