AbstractBinder's afterPropertiesSet() is now final

- subclasses should implement the new onInit() method instead of overriding
- avoids the potential for a NPE in case an overriding subclass did not call the superclass method

spring-cloud-stream-binders/spring-cloud-stream-binder-rabbit/src/main/java/org/springframework/cloud/stream/binder/rabbit/RabbitMessageChannelBinder.java

@@ -393,8 +393,7 @@ public class RabbitMessageChannelBinder extends AbstractBinder<MessageChannel> {
 	}
 
 	@Override
-	public void afterPropertiesSet() throws Exception {
-		super.afterPropertiesSet();
+	public void onInit() {
 		if (this.clustered) {
 			Assert.state(this.addresses.length == this.adminAddresses.length
 					&& this.addresses.length == this.nodes.length,