diff --git a/spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/DefaultStompSession.java b/spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/DefaultStompSession.java
index 1fd99869e3..6b378c3c36 100644
--- a/spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/DefaultStompSession.java
+++ b/spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/DefaultStompSession.java
@@ -34,7 +34,7 @@ import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageDeliveryException;
 import org.springframework.messaging.converter.MessageConversionException;
 import org.springframework.messaging.converter.MessageConverter;
-import org.springframework.messaging.converter.StringMessageConverter;
+import org.springframework.messaging.converter.SimpleMessageConverter;
 import org.springframework.messaging.support.MessageBuilder;
 import org.springframework.messaging.support.MessageHeaderAccessor;
 import org.springframework.messaging.tcp.TcpConnection;
@@ -82,7 +82,7 @@ public class DefaultStompSession implements ConnectionHandlingStompSession {
 
 	private final SettableListenableFuture<StompSession> sessionFuture = new SettableListenableFuture<StompSession>();
 
-	private MessageConverter converter = new StringMessageConverter();
+	private MessageConverter converter = new SimpleMessageConverter();
 
 	private TaskScheduler taskScheduler;
 
@@ -141,7 +141,7 @@ public class DefaultStompSession implements ConnectionHandlingStompSession {
 	 * Set the {@link MessageConverter} to use to convert the payload of incoming
 	 * and outgoing messages to and from {@code byte[]} based on object type, or
 	 * expected object type, and the "content-type" header.
-	 * <p>By default, {@link StringMessageConverter} is configured.
+	 * <p>By default, {@link SimpleMessageConverter} is configured.
 	 * @param messageConverter the message converter to use
 	 */
 	public void setMessageConverter(MessageConverter messageConverter) {
@@ -415,7 +415,8 @@ public class DefaultStompSession implements ConnectionHandlingStompSession {
 		Class<?> payloadType = ResolvableType.forType(type).getRawClass();
 		Object object = getMessageConverter().fromMessage(message, payloadType);
 		if (object == null) {
-			throw new MessageConversionException("No suitable converter, payloadType=" + payloadType);
+			throw new MessageConversionException("No suitable converter, payloadType=" + payloadType +
+					", handlerType=" + handler.getClass());
 		}
 		handler.handleFrame(stompHeaders, object);
 	}
diff --git a/spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/StompClientSupport.java b/spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/StompClientSupport.java
index ecd6d6c6ae..6cc90e9188 100644
--- a/spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/StompClientSupport.java
+++ b/spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/StompClientSupport.java
@@ -18,7 +18,7 @@ package org.springframework.messaging.simp.stomp;
 import java.util.Arrays;
 
 import org.springframework.messaging.converter.MessageConverter;
-import org.springframework.messaging.converter.StringMessageConverter;
+import org.springframework.messaging.converter.SimpleMessageConverter;
 import org.springframework.scheduling.TaskScheduler;
 import org.springframework.util.Assert;
 
@@ -41,7 +41,7 @@ import org.springframework.util.Assert;
  */
 public abstract class StompClientSupport {
 
-	private MessageConverter messageConverter = new StringMessageConverter();
+	private MessageConverter messageConverter = new SimpleMessageConverter();
 
 	private TaskScheduler taskScheduler;
 
@@ -54,7 +54,7 @@ public abstract class StompClientSupport {
 	 * Set the {@link MessageConverter} to use to convert the payload of incoming
 	 * and outgoing messages to and from {@code byte[]} based on object type
 	 * and the "content-type" header.
-	 * <p>By default, {@link StringMessageConverter} is configured.
+	 * <p>By default, {@link SimpleMessageConverter} is configured.
 	 * @param messageConverter the message converter to use
 	 */
 	public void setMessageConverter(MessageConverter messageConverter) {
diff --git a/spring-websocket/src/main/java/org/springframework/web/socket/messaging/DefaultSimpUserRegistry.java b/spring-websocket/src/main/java/org/springframework/web/socket/messaging/DefaultSimpUserRegistry.java
index e25a9b8d52..4cd575bdbb 100644
--- a/spring-websocket/src/main/java/org/springframework/web/socket/messaging/DefaultSimpUserRegistry.java
+++ b/spring-websocket/src/main/java/org/springframework/web/socket/messaging/DefaultSimpUserRegistry.java
@@ -178,7 +178,7 @@ public class DefaultSimpUserRegistry implements SimpUserRegistry, SmartApplicati
 
 		@Override
 		public SimpSession getSession(String sessionId) {
-			return this.sessions.get(sessionId);
+			return (sessionId != null ? this.sessions.get(sessionId) : null);
 		}
 
 		@Override
diff --git a/spring-websocket/src/test/java/org/springframework/web/socket/messaging/DefaultSimpUserRegistryTests.java b/spring-websocket/src/test/java/org/springframework/web/socket/messaging/DefaultSimpUserRegistryTests.java
index a176e40a02..cbccc5a567 100644
--- a/spring-websocket/src/test/java/org/springframework/web/socket/messaging/DefaultSimpUserRegistryTests.java
+++ b/spring-websocket/src/test/java/org/springframework/web/socket/messaging/DefaultSimpUserRegistryTests.java
@@ -162,6 +162,21 @@ public class DefaultSimpUserRegistryTests {
 		assertEquals(new HashSet<>(Arrays.asList("sub1", "sub2")), sessionIds);
 	}
 
+	@Test
+	public void nullSessionId() throws Exception {
+
+		DefaultSimpUserRegistry registry = new DefaultSimpUserRegistry();
+
+		TestPrincipal user = new TestPrincipal("joe");
+		Message<byte[]> message = createMessage(SimpMessageType.CONNECT_ACK, "123");
+		SessionConnectedEvent event = new SessionConnectedEvent(this, message, user);
+		registry.onApplicationEvent(event);
+
+		SimpUser simpUser = registry.getUser("joe");
+		assertNull(simpUser.getSession(null));
+	}
+
+
 	private Message<byte[]> createMessage(SimpMessageType type, String sessionId) {
 		return createMessage(type, sessionId, null, null);
 	}