Check hasNext on sessionIds in UserDestinationResult

Closes gh-34333

Signed-off-by: Branden Clark <brandenrayclark@gmail.com>

spring-messaging/src/main/java/org/springframework/messaging/simp/user/UserDestinationMessageHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,7 +20,6 @@ import java.util.Arrays;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
-import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 
 import org.apache.commons.logging.Log;
@@ -280,12 +279,10 @@ public class UserDestinationMessageHandler implements MessageHandler, SmartLifec
 			return this.messagingTemplate;
 		}
 
-		public void send(UserDestinationResult destinationResult, Message<?> message) throws MessagingException {
-			Set<String> sessionIds = destinationResult.getSessionIds();
-			Iterator<String> itr = (sessionIds != null ? sessionIds.iterator() : null);
-
-			for (String target : destinationResult.getTargetDestinations()) {
-				String sessionId = (itr != null ? itr.next() : null);
+		public void send(UserDestinationResult result, Message<?> message) throws MessagingException {
+			Iterator<String> itr = result.getSessionIds().iterator();
+			for (String target : result.getTargetDestinations()) {
+				String sessionId = (itr.hasNext() ? itr.next() : null);
 				getTemplateToUse(sessionId).send(target, message);
 			}
 		}

spring-messaging/src/main/java/org/springframework/messaging/simp/user/UserDestinationResult.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -44,7 +44,11 @@ public class UserDestinationResult {
 	private final Set<String> sessionIds;
 
 
-	public UserDestinationResult(String sourceDestination, Set<String> targetDestinations,
+	/**
+	 * Main constructor.
+	 */
+	public UserDestinationResult(
+			String sourceDestination, Set<String> targetDestinations,
 			String subscribeDestination, @Nullable String user) {
 
 		this(sourceDestination, targetDestinations, subscribeDestination, user, null);
@@ -114,7 +118,6 @@ public class UserDestinationResult {
 	/**
 	 * Return the session id for the targetDestination.
 	 */
-	@Nullable
 	public Set<String> getSessionIds() {
 		return this.sessionIds;
 	}

spring-messaging/src/test/java/org/springframework/messaging/simp/user/UserDestinationMessageHandlerTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@
 package org.springframework.messaging.simp.user;
 
 import java.nio.charset.StandardCharsets;
+import java.util.Set;
 
 import org.junit.jupiter.api.Test;
 import org.mockito.ArgumentCaptor;
@@ -98,6 +99,26 @@ class UserDestinationMessageHandlerTests {
 		assertThat(accessor.getFirstNativeHeader(ORIGINAL_DESTINATION)).isEqualTo("/user/queue/foo");
 	}
 
+	@Test
+	@SuppressWarnings("rawtypes")
+	void handleMessageWithoutSessionIds() {
+		UserDestinationResolver resolver = mock();
+		Message message = createWith(SimpMessageType.MESSAGE, "joe", null, "/user/joe/queue/foo");
+		UserDestinationResult result = new UserDestinationResult("/queue/foo-user123", Set.of("/queue/foo-user123"), "/user/queue/foo", "joe");
+		given(resolver.resolveDestination(message)).willReturn(result);
+
+		given(this.brokerChannel.send(Mockito.any(Message.class))).willReturn(true);
+		UserDestinationMessageHandler handler = new UserDestinationMessageHandler(new StubMessageChannel(), this.brokerChannel, resolver);
+		handler.handleMessage(message);
+
+		ArgumentCaptor<Message> captor = ArgumentCaptor.forClass(Message.class);
+		Mockito.verify(this.brokerChannel).send(captor.capture());
+
+		SimpMessageHeaderAccessor accessor = SimpMessageHeaderAccessor.wrap(captor.getValue());
+		assertThat(accessor.getDestination()).isEqualTo("/queue/foo-user123");
+		assertThat(accessor.getFirstNativeHeader(ORIGINAL_DESTINATION)).isEqualTo("/user/queue/foo");
+	}
+
 	@Test
 	@SuppressWarnings("rawtypes")
 	void handleMessageWithoutActiveSession() {