JpaFlowExecutionListener shouldn't assume that EntityManager is Serializable

JpaFlowExecutionListener stores EntityManager into Flow Scope, assuming it will be Serializable (each object stored into this scope should be Serializable, according to the documentation). This assumption is wrong, EntityManager doesn't extend Serializable, and doesn't have to implement this interface.

Using EclipseLink 2.2 I'm getting following exception in this case:

org.springframework.webflow.execution.repository.snapshot.SnapshotCreationException: Could not serialize flow execution; make sure all objects stored in flow or flash scope are serializable
org.springframework.webflow.execution.repository.snapshot.SerializedFlowExecutionSnapshot.<init>(SerializedFlowExecutionSnapshot.java:75)
org.springframework.webflow.execution.repository.snapshot.SerializedFlowExecutionSnapshotFactory.createSnapshot(SerializedFlowExecutionSnapshotFactory.java:70)
org.springframework.webflow.execution.repository.snapshot.AbstractSnapshottingFlowExecutionRepository.snapshot(AbstractSnapshottingFlowExecutionRepository.java:75)
org.springframework.webflow.execution.repository.impl.DefaultFlowExecutionRepository.putFlowExecution(DefaultFlowExecutionRepository.java:126)
org.springframework.webflow.executor.FlowExecutorImpl.launchExecution(FlowExecutorImpl.java:145)
org.springframework.webflow.mvc.servlet.FlowHandlerAdapter.handle(FlowHandlerAdapter.java:193)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)
...
java.io.NotSerializableException: org.eclipse.persistence.internal.jpa.EntityManagerImpl
java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1164)
java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1518)
java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1483)
java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1400)
...
java.util.HashMap.writeObject(HashMap.java:1001)
...
org.springframework.webflow.core.collection.LocalAttributeMap.writeObject(LocalAttributeMap.java:327)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
...
org.springframework.webflow.engine.impl.FlowSessionImpl.writeExternal(FlowSessionImpl.java:154)
...
org.springframework.webflow.engine.impl.FlowExecutionImpl.writeExternal(FlowExecutionImpl.java:312)
...
org.springframework.webflow.execution.repository.snapshot.SerializedFlowExecutionSnapshot.serialize(SerializedFlowExecutionSnapshot.java:173)
org.springframework.webflow.execution.repository.snapshot.SerializedFlowExecutionSnapshot.<init>(SerializedFlowExecutionSnapshot.java:70)
org.springframework.webflow.execution.repository.snapshot.SerializedFlowExecutionSnapshotFactory.createSnapshot(SerializedFlowExecutionSnapshotFactory.java:70)
org.springframework.webflow.execution.repository.snapshot.AbstractSnapshottingFlowExecutionRepository.snapshot(AbstractSnapshottingFlowExecutionRepository.java:75)
org.springframework.webflow.execution.repository.impl.DefaultFlowExecutionRepository.putFlowExecution(DefaultFlowExecutionRepository.java:126)
org.springframework.webflow.executor.FlowExecutorImpl.launchExecution(FlowExecutorImpl.java:145)
org.springframework.webflow.mvc.servlet.FlowHandlerAdapter.handle(FlowHandlerAdapter.java:193)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)