SensingNullMessageProcessor flowListener = new SensingNullMessageProcessor();
Flow flow = new Flow("flow", muleContext);
flow.setMessageProcessors(Collections.<MessageProcessor> singletonList(flowListener));
flow.initialise();
flow.start();
Object nonSerializable = new Object();
event.getSession().setProperty("key", "value");
event.getSession().setProperty("key2", nonSerializable);