GH-1166: Fix NPE in RepublishMessageRecoverer

Resolves #1166

Occurred when the cause had a `null` message.

Author: garyrussell

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/retry/RepublishMessageRecoverer.java

@@ -209,7 +209,7 @@ private String[] processStackTrace(Throwable cause, String exceptionMessage) {
 	private String[] truncateIfNecessary(Throwable cause, String exception, String stackTrace) {
 		boolean truncated = false;
 		String stackTraceAsString = stackTrace;
-		String exceptionMessage = exception;
+		String exceptionMessage = exception == null ? "" : exception;
 		String truncatedExceptionMessage = exceptionMessage.length() <= MAX_EXCEPTION_MESSAGE_SIZE_IN_TRACE
 				? exceptionMessage
 				: (exceptionMessage.substring(0, MAX_EXCEPTION_MESSAGE_SIZE_IN_TRACE) + "...");

spring-rabbit/src/test/java/org/springframework/amqp/rabbit/retry/RepublishMessageRecovererTest.java

@@ -54,28 +54,36 @@ public class RepublishMessageRecovererTest {
 	private RepublishMessageRecoverer recoverer;
 
 	@BeforeEach
-	public void beforeEach() {
+	void beforeEach() {
 		message.getMessageProperties().setReceivedRoutingKey("some.key");
 	}
 
 	@Test
-	public void shouldPublishWithRoutingKeyPrefixedWithErrorWhenExchangeIsNotSet() {
+	void shouldPublishWithRoutingKeyPrefixedWithErrorWhenExchangeIsNotSet() {
 		recoverer = new RepublishMessageRecoverer(amqpTemplate);
 		recoverer.recover(message, cause);
 
 		verify(amqpTemplate).send("error.some.key", message);
 	}
 
 	@Test
-	public void shouldPublishWithSetErrorRoutingKeyWhenExchangeAndErrorRoutingKeyProvided() {
+	void nullCauseMessage() {
+		recoverer = new RepublishMessageRecoverer(amqpTemplate);
+		recoverer.recover(message, new RuntimeException(new RuntimeException()));
+
+		verify(amqpTemplate).send("error.some.key", message);
+	}
+
+	@Test
+	void shouldPublishWithSetErrorRoutingKeyWhenExchangeAndErrorRoutingKeyProvided() {
 		recoverer = new RepublishMessageRecoverer(amqpTemplate, "errorExchange", "errorRoutingKey");
 		recoverer.recover(message, cause);
 
 		verify(amqpTemplate).send("errorExchange", "errorRoutingKey", message);
 	}
 
 	@Test
-	public void shouldPublishToProvidedExchange() {
+	void shouldPublishToProvidedExchange() {
 		recoverer = new RepublishMessageRecoverer(amqpTemplate, "error");
 
 		recoverer.recover(message, cause);
@@ -84,7 +92,7 @@ public void shouldPublishToProvidedExchange() {
 	}
 
 	@Test
-	public void shouldIncludeTheStacktraceInTheHeaderOfThePublishedMessage() {
+	void shouldIncludeTheStacktraceInTheHeaderOfThePublishedMessage() {
 		recoverer = new RepublishMessageRecoverer(amqpTemplate);
 		ByteArrayOutputStream baos = new ByteArrayOutputStream();
 		cause.printStackTrace(new PrintStream(baos));
@@ -96,15 +104,15 @@ public void shouldIncludeTheStacktraceInTheHeaderOfThePublishedMessage() {
 	}
 
 	@Test
-	public void shouldIncludeTheCauseMessageInTheHeaderOfThePublishedMessage() {
+	void shouldIncludeTheCauseMessageInTheHeaderOfThePublishedMessage() {
 		recoverer = new RepublishMessageRecoverer(amqpTemplate);
 		recoverer.recover(message, cause);
 
 		assertThat(message.getMessageProperties().getHeaders().get("x-exception-message")).isEqualTo(cause.getCause().getMessage());
 	}
 
 	@Test
-	public void shouldSetTheOriginalMessageExchangeOnInTheHeaders() {
+	void shouldSetTheOriginalMessageExchangeOnInTheHeaders() {
 		message.getMessageProperties().setReceivedExchange("the.original.exchange");
 		recoverer = new RepublishMessageRecoverer(amqpTemplate, "error");
 
@@ -114,7 +122,7 @@ public void shouldSetTheOriginalMessageExchangeOnInTheHeaders() {
 	}
 
 	@Test
-	public void shouldRemapDeliveryMode() {
+	void shouldRemapDeliveryMode() {
 		message.getMessageProperties().setDeliveryMode(null);
 		message.getMessageProperties().setReceivedDeliveryMode(MessageDeliveryMode.PERSISTENT);
 		recoverer = new RepublishMessageRecoverer(amqpTemplate, "error") {
@@ -133,7 +141,7 @@ public void shouldRemapDeliveryMode() {
 	}
 
 	@Test
-	public void setDeliveryModeIfNull() {
+	void setDeliveryModeIfNull() {
 		this.message.getMessageProperties().setDeliveryMode(null);
 		this.recoverer = new RepublishMessageRecoverer(amqpTemplate, "error");