Fixed accidental use of Reactor's Assert util

Issue: SPR-10880

spring-messaging/src/main/java/org/springframework/messaging/simp/config/AbstractBrokerRegistration.java

@@ -22,9 +22,7 @@ import java.util.Collections;
 
 import org.springframework.messaging.MessageChannel;
 import org.springframework.messaging.simp.handler.AbstractBrokerMessageHandler;
-
-import reactor.util.Assert;
-
+import org.springframework.util.Assert;
 
 /**
  * Base class for message broker registration classes.

spring-messaging/src/main/java/org/springframework/messaging/simp/config/MessageBrokerConfigurer.java

@@ -21,9 +21,7 @@ import java.util.Collection;
 
 import org.springframework.messaging.MessageChannel;
 import org.springframework.messaging.simp.handler.AbstractBrokerMessageHandler;
-
-import reactor.util.Assert;
-
+import org.springframework.util.Assert;
 
 /**
  * A helper class for configuring message broker options.

spring-messaging/src/main/java/org/springframework/messaging/simp/handler/DefaultSubscriptionRegistry.java

@@ -26,12 +26,10 @@ import java.util.concurrent.CopyOnWriteArraySet;
 
 import org.springframework.messaging.Message;
 import org.springframework.util.AntPathMatcher;
+import org.springframework.util.Assert;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 
-import reactor.util.Assert;
-
-
 /**
  * @author Rossen Stoyanchev
  * @since 4.0

spring-messaging/src/test/java/org/springframework/messaging/simp/stomp/StompBrokerRelayMessageHandlerIntegrationTests.java

@@ -30,6 +30,7 @@ import org.apache.commons.logging.LogFactory;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
+
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.messaging.Message;
@@ -38,13 +39,11 @@ import org.springframework.messaging.MessagingException;
 import org.springframework.messaging.simp.BrokerAvailabilityEvent;
 import org.springframework.messaging.support.MessageBuilder;
 import org.springframework.messaging.support.channel.ExecutorSubscribableChannel;
+import org.springframework.util.Assert;
 import org.springframework.util.SocketUtils;
 
-import reactor.util.Assert;
-
 import static org.junit.Assert.*;
 
-
 /**
  * @author Rossen Stoyanchev
  */