Remove erroneous @nullable

Incorrectly added to message converter.

Author: garyrussell

spring-amqp/src/main/java/org/springframework/amqp/support/converter/MessageConverter.java

@@ -62,7 +62,6 @@ default Message toMessage(Object object, MessageProperties messageProperties, @N
 	 * @return the converted Java object
 	 * @throws MessageConversionException in case of conversion failure
 	 */
-	@Nullable
 	Object fromMessage(Message message) throws MessageConversionException;
 
 }

spring-amqp/src/main/java/org/springframework/amqp/support/converter/MessagingMessageConverter.java

@@ -22,7 +22,6 @@
 import org.springframework.amqp.support.AmqpHeaderMapper;
 import org.springframework.amqp.support.SimpleAmqpHeaderMapper;
 import org.springframework.beans.factory.InitializingBean;
-import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.support.MessageBuilder;
 import org.springframework.util.Assert;
@@ -131,7 +130,6 @@ public Object fromMessage(org.springframework.amqp.core.Message message) throws
 	 * @param message the AMQP Message to extract {@code payload}.
 	 * @return the extracted {@code payload}.
 	 */
-	@Nullable
 	protected Object extractPayload(org.springframework.amqp.core.Message message) {
 		return this.payloadConverter.fromMessage(message);
 	}

spring-amqp/src/main/java/org/springframework/amqp/support/converter/RemoteInvocationAwareMessageConverterAdapter.java

@@ -20,7 +20,6 @@
 import org.springframework.amqp.core.Message;
 import org.springframework.amqp.core.MessageProperties;
 import org.springframework.beans.factory.BeanClassLoaderAware;
-import org.springframework.lang.Nullable;
 import org.springframework.remoting.support.RemoteInvocationResult;
 import org.springframework.util.Assert;
 
@@ -63,12 +62,14 @@ public Message toMessage(Object object, MessageProperties messageProperties) thr
 	}
 
 	@Override
-	@Nullable
 	public Object fromMessage(Message message) throws MessageConversionException {
 		Object result = this.delegate.fromMessage(message);
 		if (result instanceof RemoteInvocationResult) {
 			try {
 				result = ((RemoteInvocationResult) result).recreate();
+				if (result == null) {
+					throw new MessageConversionException("RemoteInvocationResult returned null");
+				}
 			}
 			catch (Throwable e) { // NOSONAR
 				throw new AmqpRemoteException(e);