INT-4500: Fix DefAmqpHeaderMapper correlationId

JIRA https://jira.spring.io/browse/INT-4500

The `correlationId` condition was against a `contentType` by mistake

* Code style polishing, add `@author`

(cherry picked from commit 0dcbde0)

Author: ssinger

spring-integration-amqp/src/main/java/org/springframework/integration/amqp/support/DefaultAmqpHeaderMapper.java

@@ -50,11 +50,13 @@
  * @author Gary Russell
  * @author Artem Bilan
  * @author Stephane Nicoll
+ * @author Steve Singer
+ *
  * @since 2.1
  */
 public class DefaultAmqpHeaderMapper extends AbstractHeaderMapper<MessageProperties> implements AmqpHeaderMapper {
 
-	private static final List<String> STANDARD_HEADER_NAMES = new ArrayList<String>();
+	private static final List<String> STANDARD_HEADER_NAMES = new ArrayList<>();
 
 	static {
 		STANDARD_HEADER_NAMES.add(AmqpHeaders.APP_ID);
@@ -123,7 +125,7 @@ protected Map<String, Object> extractStandardHeaders(MessageProperties amqpMessa
 				headers.put(AmqpHeaders.CONTENT_TYPE, contentType);
 			}
 			String correlationId = amqpMessageProperties.getCorrelationId();
-			if (StringUtils.hasText(contentType)) {
+			if (StringUtils.hasText(correlationId)) {
 				headers.put(AmqpHeaders.CORRELATION_ID, correlationId);
 			}
 			MessageDeliveryMode receivedDeliveryMode = amqpMessageProperties.getReceivedDeliveryMode();

spring-integration-amqp/src/test/java/org/springframework/integration/amqp/support/DefaultAmqpHeaderMapperTests.java

@@ -46,6 +46,8 @@
  * @author Oleg Zhurakousky
  * @author Stephane Nicoll
  * @author Artem Bilan
+ * @author Steve Singer
+ *
  * @since 2.1
  */
 public class DefaultAmqpHeaderMapperTests {
@@ -201,6 +203,20 @@ public void toHeaders() {
 		assertEquals("test.replyTo2", headerMap.get(AmqpHeaders.SPRING_REPLY_TO_STACK));
 	}
 
+	@Test
+	public void toHeadersNonContenType() {
+		DefaultAmqpHeaderMapper headerMapper = DefaultAmqpHeaderMapper.inboundMapper();
+		MessageProperties amqpProperties = new MessageProperties();
+		amqpProperties.setAppId("test.appId");
+		amqpProperties.setClusterId("test.clusterId");
+		amqpProperties.setContentType(null);
+		String testCorrelationId = "foo";
+		amqpProperties.setCorrelationId(testCorrelationId);
+		Map<String, Object> headerMap = headerMapper.toHeadersFromReply(amqpProperties);
+		assertEquals(testCorrelationId, headerMap.get(AmqpHeaders.CORRELATION_ID));
+	}
+
+
 	@Test
 	public void testToHeadersConsumerMetadata() {
 		DefaultAmqpHeaderMapper headerMapper = DefaultAmqpHeaderMapper.inboundMapper();