Avoid earlyApplicationEvents iteration in case of empty Set

Closes gh-25161

Author: jhoeller

spring-context/src/main/java/org/springframework/context/support/AbstractApplicationContext.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -79,6 +79,7 @@
 import org.springframework.core.io.support.ResourcePatternResolver;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.ReflectionUtils;
 
@@ -836,7 +837,7 @@ protected void registerListeners() {
 		// Publish early application events now that we finally have a multicaster...
 		Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
 		this.earlyApplicationEvents = null;
-		if (earlyEventsToProcess != null) {
+		if (!CollectionUtils.isEmpty(earlyEventsToProcess)) {
 			for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
 				getApplicationEventMulticaster().multicastEvent(earlyEvent);
 			}