Fixed assert in setAspectJAdvisorFactory()

Issue: SPR-11330

spring-aop/src/main/java/org/springframework/aop/aspectj/annotation/AnnotationAwareAspectJAutoProxyCreator.java

 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2013 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.
@@ -67,7 +67,7 @@ public class AnnotationAwareAspectJAutoProxyCreator extends AspectJAwareAdvisorA
 	}
 
 	public void setAspectJAdvisorFactory(AspectJAdvisorFactory aspectJAdvisorFactory) {
-		Assert.notNull(this.aspectJAdvisorFactory, "AspectJAdvisorFactory must not be null");
+		Assert.notNull(aspectJAdvisorFactory, "AspectJAdvisorFactory must not be null");
 		this.aspectJAdvisorFactory = aspectJAdvisorFactory;
 	}