Fix internal transition for dist machine

- Change previous DistributedStateMachine fixes which didn't
  really work. Now explicitely getting state from machine to be set
  into ensemble for post internal transition.
- Now can send Message<E> via test plan instead of plain E.
- More testing for tweaked features.

spring-statemachine-core/src/main/java/org/springframework/statemachine/ensemble/DistributedStateMachine.java

@@ -219,11 +219,14 @@ public class DistributedStateMachine<S, E> extends LifecycleObjectSupport implem
 							stateContext.getMessageHeader(StateMachineSystemConstants.STATEMACHINE_IDENTIFIER))) {
 				StateMachineContext<S, E> current = ensemble.getState();
 				if (current != null) {
-					// TODO: it feels a bit wrong that this can be null so
-					//       adding note here. feel this will come back to haunt us
 					ensemble.setState(new DefaultStateMachineContext<S, E>(
 							current.getState(), stateContext.getEvent(), stateContext
 									.getMessageHeaders(), stateContext.getStateMachine().getExtendedState()));
+				} else if (stateContext.getStateMachine().getState() != null) {
+					// if current ensemble state is null, get it from sm itself
+					ensemble.setState(new DefaultStateMachineContext<S, E>(stateContext.getStateMachine().getState()
+							.getId(), stateContext.getEvent(), stateContext.getMessageHeaders(), stateContext
+							.getStateMachine().getExtendedState()));
 				}
 			}
 			return stateContext;