Add checks for missing transitions

- Now checking if some transitions are missing
  and throwing a proper exception instead of NPE.
- Fixes #775

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

@@ -46,6 +46,7 @@ import org.springframework.statemachine.config.model.EntryData;
 import org.springframework.statemachine.config.model.ExitData;
 import org.springframework.statemachine.config.model.HistoryData;
 import org.springframework.statemachine.config.model.JunctionData;
+import org.springframework.statemachine.config.model.MalformedConfigurationException;
 import org.springframework.statemachine.config.model.StateData;
 import org.springframework.statemachine.config.model.StateMachineModel;
 import org.springframework.statemachine.config.model.StateMachineModelFactory;
@@ -665,6 +666,9 @@ public abstract class AbstractStateMachineFactory<S, E> extends LifecycleObjectS
 				State<S, E> defaultState = null;
 				S s = stateData.getState();
 				Collection<HistoryData<S,E>> historys = stateMachineTransitions.getHistorys();
+				if (historys == null) {
+					throw new MalformedConfigurationException("No transitions for state " + s);
+				}
 				for (HistoryData<S,E> history : historys) {
 					if (history.getSource().equals(s)) {
 						defaultState = stateMap.get(history.getTarget());
@@ -685,6 +689,9 @@ public abstract class AbstractStateMachineFactory<S, E> extends LifecycleObjectS
 				State<S, E> defaultState = null;
 				S s = stateData.getState();
 				Collection<HistoryData<S,E>> historys = stateMachineTransitions.getHistorys();
+				if (historys == null) {
+					throw new MalformedConfigurationException("No transitions for state " + s);
+				}
 				for (HistoryData<S,E> history : historys) {
 					if (history.getSource().equals(s)) {
 						defaultState = stateMap.get(history.getTarget());
@@ -706,6 +713,9 @@ public abstract class AbstractStateMachineFactory<S, E> extends LifecycleObjectS
 			if (stateData.getPseudoStateKind() == PseudoStateKind.CHOICE) {
 				S s = stateData.getState();
 				List<ChoiceData<S, E>> list = stateMachineTransitions.getChoices().get(s);
+				if (list == null) {
+					throw new MalformedConfigurationException("No transitions for state " + s);
+				}
 				List<ChoiceStateData<S, E>> choices = new ArrayList<ChoiceStateData<S, E>>();
 				for (ChoiceData<S, E> c : list) {
 					StateHolder<S, E> holder = new StateHolder<S, E>(stateMap.get(c.getTarget()));
@@ -723,6 +733,9 @@ public abstract class AbstractStateMachineFactory<S, E> extends LifecycleObjectS
 				S s = stateData.getState();
 				List<JunctionData<S, E>> list = stateMachineTransitions.getJunctions().get(s);
 				List<JunctionStateData<S, E>> junctions = new ArrayList<JunctionStateData<S, E>>();
+				if (list == null) {
+					throw new MalformedConfigurationException("No transitions for state " + s);
+				}
 				for (JunctionData<S, E> c : list) {
 					StateHolder<S, E> holder = new StateHolder<S, E>(stateMap.get(c.getTarget()));
 					if (holder.getState() == null) {
@@ -738,6 +751,9 @@ public abstract class AbstractStateMachineFactory<S, E> extends LifecycleObjectS
 			} else if (stateData.getPseudoStateKind() == PseudoStateKind.ENTRY) {
 				S s = stateData.getState();
 				Collection<EntryData<S, E>> entrys = stateMachineTransitions.getEntrys();
+				if (entrys == null) {
+					throw new MalformedConfigurationException("No transitions for state " + s);
+				}
 				for (EntryData<S, E> entry : entrys) {
 					if (s.equals(entry.getSource())) {
 						PseudoState<S, E> pseudoState = new EntryPseudoState<S, E>(stateMap.get(entry.getTarget()));
@@ -751,6 +767,9 @@ public abstract class AbstractStateMachineFactory<S, E> extends LifecycleObjectS
 			} else if (stateData.getPseudoStateKind() == PseudoStateKind.EXIT) {
 				S s = stateData.getState();
 				Collection<ExitData<S, E>> exits = stateMachineTransitions.getExits();
+				if (exits == null) {
+					throw new MalformedConfigurationException("No transitions for state " + s);
+				}
 				for (ExitData<S, E> entry : exits) {
 					if (s.equals(entry.getSource())) {
 						StateHolder<S, E> holder = new StateHolder<S, E>(stateMap.get(entry.getTarget()));
@@ -769,6 +788,9 @@ public abstract class AbstractStateMachineFactory<S, E> extends LifecycleObjectS
 				S s = stateData.getState();
 				List<S> list = stateMachineTransitions.getForks().get(s);
 				List<State<S, E>> forks = new ArrayList<State<S,E>>();
+				if (list == null) {
+					throw new MalformedConfigurationException("No transitions for state " + s);
+				}
 				for (S fs : list) {
 					forks.add(stateMap.get(fs));
 				}
@@ -780,6 +802,9 @@ public abstract class AbstractStateMachineFactory<S, E> extends LifecycleObjectS
 			} else if (stateData.getPseudoStateKind() == PseudoStateKind.JOIN) {
 				S s = stateData.getState();
 				List<S> list = stateMachineTransitions.getJoins().get(s);
+				if (list == null) {
+					throw new MalformedConfigurationException("No transitions for state " + s);
+				}
 				List<List<State<S, E>>> joins = new ArrayList<List<State<S, E>>>();
 
 				// if join source is an orthogonal state, assume we're joining by region end states

spring-statemachine-core/src/test/java/org/springframework/statemachine/config/ConfigurationErrorTests.java

@@ -15,6 +15,7 @@
  */
 package org.springframework.statemachine.config;
 
+import static org.hamcrest.CoreMatchers.containsString;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
 import static org.junit.jupiter.api.Assertions.assertThrows;
@@ -121,6 +122,26 @@ public class ConfigurationErrorTests extends AbstractStateMachineTests {
 		assertThat(verifier.latch.await(2, TimeUnit.SECONDS), is(true));
 	}
 
+	@Test
+	public void testPseudostateNoTransition() throws Exception {
+		Exception exception = assertThrows(Exception.class, ()-> {
+			Builder<String, String> builder = StateMachineBuilder.builder();
+			builder.configureStates()
+				.withStates()
+					.initial("S1")
+					.state("S1")
+					.choice("S2")
+					.state("S3");
+			builder.configureTransitions()
+				.withExternal()
+					.source("S1")
+					.target("S2");
+			builder.build();
+		});
+		assertTrue(exception.getCause() instanceof MalformedConfigurationException);
+		assertThat(exception.getLocalizedMessage(), containsString("No transitions for state S2"));
+	}
+
 	@Configuration
 	@EnableStateMachine
 	public static class Config1 extends StateMachineConfigurerAdapter<String, String> {