Fix npe with choice

- Preventing passing nulls into factory if choice configurer
  only have last() defined.
- Polish some classes around those classes.
- Fixes #101

spring-statemachine-core/src/main/java/org/springframework/statemachine/config/builders/StateMachineTransitions.java

@@ -33,11 +33,19 @@ import org.springframework.statemachine.transition.TransitionKind;
  */
 public class StateMachineTransitions<S, E> {
 
-	private Collection<TransitionData<S, E>> transitions;
-	private Map<S, List<ChoiceData<S, E>>> choices;
-	private Map<S, List<S>> forks;
-	private Map<S, List<S>> joins;
+	private final Collection<TransitionData<S, E>> transitions;
+	private final Map<S, List<ChoiceData<S, E>>> choices;
+	private final Map<S, List<S>> forks;
+	private final Map<S, List<S>> joins;
 
+	/**
+	 * Instantiates a new state machine transitions.
+	 *
+	 * @param transitions the transitions
+	 * @param choices the choices
+	 * @param forks the forks
+	 * @param joins the joins
+	 */
 	public StateMachineTransitions(Collection<TransitionData<S, E>> transitions,
 			Map<S, List<ChoiceData<S, E>>> choices, Map<S, List<S>> forks, Map<S, List<S>> joins) {
 		this.transitions = transitions;
@@ -46,32 +54,72 @@ public class StateMachineTransitions<S, E> {
 		this.joins = joins;
 	}
 
+	/**
+	 * Gets the transitions.
+	 *
+	 * @return the transitions
+	 */
 	public Collection<TransitionData<S, E>> getTransitions() {
 		return transitions;
 	}
 
+	/**
+	 * Gets the choices.
+	 *
+	 * @return the choices
+	 */
 	public Map<S, List<ChoiceData<S, E>>> getChoices() {
 		return choices;
 	}
 
+	/**
+	 * Gets the forks.
+	 *
+	 * @return the forks
+	 */
 	public Map<S, List<S>> getForks() {
 		return forks;
 	}
 
+	/**
+	 * Gets the joins.
+	 *
+	 * @return the joins
+	 */
 	public Map<S, List<S>> getJoins() {
 		return joins;
 	}
 
+	/**
+	 * A simple data object keeping transition related configs in a same place.
+	 *
+	 * @param <S> the type of state
+	 * @param <E> the type of event
+	 */
 	public static class TransitionData<S, E> {
-		S source;
-		S target;
-		S state;
-		E event;
-		Long period;
-		Collection<Action<S, E>> actions;
-		Guard<S, E> guard;
-		TransitionKind kind;
-		public TransitionData(S source, S target, S state, E event, Long period, Collection<Action<S, E>> actions, Guard<S, E> guard, TransitionKind kind) {
+		private final S source;
+		private final S target;
+		private final S state;
+		private final E event;
+		private final Long period;
+		private final Collection<Action<S, E>> actions;
+		private final Guard<S, E> guard;
+		private final TransitionKind kind;
+
+		/**
+		 * Instantiates a new transition data.
+		 *
+		 * @param source the source
+		 * @param target the target
+		 * @param state the state
+		 * @param event the event
+		 * @param period the period
+		 * @param actions the actions
+		 * @param guard the guard
+		 * @param kind the kind
+		 */
+		public TransitionData(S source, S target, S state, E event, Long period, Collection<Action<S, E>> actions,
+				Guard<S, E> guard, TransitionKind kind) {
 			this.source = source;
 			this.target = target;
 			this.state = state;
@@ -81,51 +129,130 @@ public class StateMachineTransitions<S, E> {
 			this.guard = guard;
 			this.kind = kind;
 		}
+
+		/**
+		 * Gets the source.
+		 *
+		 * @return the source
+		 */
 		public S getSource() {
 			return source;
 		}
+
+		/**
+		 * Gets the target.
+		 *
+		 * @return the target
+		 */
 		public S getTarget() {
 			return target;
 		}
+
+		/**
+		 * Gets the state.
+		 *
+		 * @return the state
+		 */
 		public S getState() {
 			return state;
 		}
+
+		/**
+		 * Gets the event.
+		 *
+		 * @return the event
+		 */
 		public E getEvent() {
 			return event;
 		}
+
+		/**
+		 * Gets the period.
+		 *
+		 * @return the period
+		 */
 		public Long getPeriod() {
 			return period;
 		}
+
+		/**
+		 * Gets the actions.
+		 *
+		 * @return the actions
+		 */
 		public Collection<Action<S, E>> getActions() {
 			return actions;
 		}
+
+		/**
+		 * Gets the guard.
+		 *
+		 * @return the guard
+		 */
 		public Guard<S, E> getGuard() {
 			return guard;
 		}
+
+		/**
+		 * Gets the kind.
+		 *
+		 * @return the kind
+		 */
 		public TransitionKind getKind() {
 			return kind;
 		}
 	}
 
+	/**
+	 * A simple data object keeping choice related configs in a same place.
+	 *
+	 * @param <S> the type of state
+	 * @param <E> the type of event
+	 */
 	public static class ChoiceData<S, E> {
 		private final S source;
 		private final S target;
 		private final Guard<S, E> guard;
+
+		/**
+		 * Instantiates a new choice data.
+		 *
+		 * @param source the source
+		 * @param target the target
+		 * @param guard the guard
+		 */
 		public ChoiceData(S source, S target, Guard<S, E> guard) {
 			this.source = source;
 			this.target = target;
 			this.guard = guard;
 		}
+
+		/**
+		 * Gets the source.
+		 *
+		 * @return the source
+		 */
 		public S getSource() {
 			return source;
 		}
+
+		/**
+		 * Gets the target.
+		 *
+		 * @return the target
+		 */
 		public S getTarget() {
 			return target;
 		}
+
+		/**
+		 * Gets the guard.
+		 *
+		 * @return the guard
+		 */
 		public Guard<S, E> getGuard() {
 			return guard;
 		}
 	}
 
-
 }

spring-statemachine-core/src/main/java/org/springframework/statemachine/config/configurers/DefaultChoiceTransitionConfigurer.java

@@ -38,19 +38,20 @@ public class DefaultChoiceTransitionConfigurer<S, E>
 		implements ChoiceTransitionConfigurer<S, E> {
 
 	private S source;
-
 	private ChoiceData<S, E> first;
-
 	private final List<ChoiceData<S, E>> thens = new ArrayList<ChoiceData<S, E>>();
-
 	private ChoiceData<S, E> last;
 
 	@Override
 	public void configure(StateMachineTransitionBuilder<S, E> builder) throws Exception {
 		List<ChoiceData<S, E>> choices = new ArrayList<ChoiceData<S, E>>();
-		choices.add(first);
+		if (first != null) {
+			choices.add(first);
+		}
 		choices.addAll(thens);
-		choices.add(last);
+		if (last != null) {
+			choices.add(last);
+		}
 		builder.add(source, choices);
 	}
 

spring-statemachine-core/src/main/java/org/springframework/statemachine/state/ChoicePseudoState.java

@@ -30,8 +30,13 @@ import org.springframework.statemachine.guard.Guard;
  */
 public class ChoicePseudoState<S, E> implements PseudoState<S, E> {
 
-	private List<ChoiceStateData<S, E>> choices;
+	private final List<ChoiceStateData<S, E>> choices;
 
+	/**
+	 * Instantiates a new choice pseudo state.
+	 *
+	 * @param choices the choices
+	 */
 	public ChoicePseudoState(List<ChoiceStateData<S, E>> choices) {
 		this.choices = choices;
 	}
@@ -52,7 +57,7 @@ public class ChoicePseudoState<S, E> implements PseudoState<S, E> {
 		}
 		return s;
 	}
-	
+
 	@Override
 	public void exit(StateContext<S, E> context) {
 	}
@@ -61,16 +66,42 @@ public class ChoicePseudoState<S, E> implements PseudoState<S, E> {
 	public void addPseudoStateListener(PseudoStateListener<S, E> listener) {
 	}
 
+	/**
+	 * Data class wrapping choice {@link State} and {@link Guard}
+	 * together.
+	 *
+	 * @param <S> the type of state
+	 * @param <E> the type of event
+	 */
 	public static class ChoiceStateData<S, E> {
 		private final State<S, E> state;
 		private final Guard<S, E> guard;
+
+		/**
+		 * Instantiates a new choice state data.
+		 *
+		 * @param state the state
+		 * @param guard the guard
+		 */
 		public ChoiceStateData(State<S, E> state, Guard<S, E> guard) {
 			this.state = state;
 			this.guard = guard;
 		}
+
+		/**
+		 * Gets the state.
+		 *
+		 * @return the state
+		 */
 		public State<S, E> getState() {
 			return state;
 		}
+
+		/**
+		 * Gets the guard.
+		 *
+		 * @return the guard
+		 */
 		public Guard<S, E> getGuard() {
 			return guard;
 		}

spring-statemachine-core/src/test/java/org/springframework/statemachine/state/ChoiceStateTests.java

@@ -100,6 +100,20 @@ public class ChoiceStateTests extends AbstractStateMachineTests {
 		assertThat(machine.getState().getIds(), contains(TestStates.S33));
 	}
 
+	@Test
+	@SuppressWarnings("unchecked")
+	public void testOnlyLast() {
+		context.register(BaseConfig.class, Config2.class);
+		context.refresh();
+		ObjectStateMachine<TestStates,TestEvents> machine =
+				context.getBean(StateMachineSystemConstants.DEFAULT_ID_STATEMACHINE, ObjectStateMachine.class);
+		assertThat(machine, notNullValue());
+		machine.start();
+		machine.sendEvent(MessageBuilder.withPayload(TestEvents.E1).build());
+
+		assertThat(machine.getState().getIds(), contains(TestStates.S33));
+	}
+
 	@Configuration
 	@EnableStateMachine
 	static class Config1 extends EnumStateMachineConfigurerAdapter<TestStates, TestEvents> {
@@ -146,6 +160,53 @@ public class ChoiceStateTests extends AbstractStateMachineTests {
 		}
 
 	}
+	@Configuration
+	@EnableStateMachine
+	static class Config2 extends EnumStateMachineConfigurerAdapter<TestStates, TestEvents> {
+
+		@Override
+		public void configure(StateMachineStateConfigurer<TestStates, TestEvents> states) throws Exception {
+			states
+				.withStates()
+					.initial(TestStates.SI)
+					.states(EnumSet.allOf(TestStates.class))
+					.choice(TestStates.S3)
+					.end(TestStates.SF);
+		}
+
+		@Override
+		public void configure(StateMachineTransitionConfigurer<TestStates, TestEvents> transitions) throws Exception {
+			transitions
+				.withExternal()
+					.source(TestStates.SI)
+					.target(TestStates.S3)
+					.event(TestEvents.E1)
+					.and()
+				.withChoice()
+					.source(TestStates.S3)
+//					.first(TestStates.S30, s30Guard())
+//					.then(TestStates.S31, s31Guard())
+//					.then(TestStates.S32, s32Guard())
+					.last(TestStates.S33);
+		}
+
+		@Bean
+		public Guard<TestStates, TestEvents> s30Guard() {
+			return new ChoiceGuard("s30");
+		}
+
+		@Bean
+		public Guard<TestStates, TestEvents> s31Guard() {
+			return new ChoiceGuard("s31");
+		}
+
+		@Bean
+		public Guard<TestStates, TestEvents> s32Guard() {
+			return new ChoiceGuard("s32");
+		}
+
+	}
+
 
 	private static class ChoiceGuard implements Guard<TestStates, TestEvents> {