Fix Sonar Issue

Author: garyrussell

spring-kafka/src/main/java/org/springframework/kafka/listener/KafkaMessageListenerContainer.java

@@ -3159,17 +3159,23 @@ private OffsetAndMetadata createOffsetAndMetadata(long offset) {
 
 		private final class ConsumerAwareListenerMetadata implements ListenerMetadata {
 
+			ConsumerAwareListenerMetadata() {
+			}
+
 			@Override
+			@Nullable
 			public String getListenerId() {
 				return getBeanName();
 			}
 
 			@Override
+			@Nullable
 			public String getGroupId() {
 				return ListenerConsumer.this.consumerGroupId;
 			}
 
 			@Override
+			@Nullable
 			public byte[] getListenerInfo() {
 				return ListenerConsumer.this.listenerinfo;
 			}

spring-kafka/src/main/java/org/springframework/kafka/listener/ListenerMetadata.java

@@ -16,10 +16,13 @@
 
 package org.springframework.kafka.listener;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Metadata associated to a {@link org.springframework.kafka.annotation.KafkaListener}.
  *
  * @author Francois Rosiere
+ * @author Gary Russell
  * @since 2.8.5
  * @see org.springframework.kafka.annotation.KafkaListener
  */
@@ -29,17 +32,21 @@ public interface ListenerMetadata {
 	 * Return the listener id.
 	 * @return the listener id.
 	 */
+	@Nullable
 	String getListenerId();
 
 	/**
 	 * Return the group id.
 	 * @return the group id.
 	 */
+	@Nullable
 	String getGroupId();
 
 	/**
 	 * Return the listener info.
 	 * @return the listener info.
 	 */
+	@Nullable
 	byte[] getListenerInfo();
+
 }