Polish AbstractAspectJAdvisorFactory

Closes gh-27340

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

@@ -103,10 +103,11 @@ public abstract class AbstractAspectJAdvisorFactory implements AspectJAdvisorFac
 	@Override
 	public void validate(Class<?> aspectClass) throws AopConfigException {
 		// If the parent has the annotation and isn't abstract it's an error
-		if (aspectClass.getSuperclass().getAnnotation(Aspect.class) != null &&
-				!Modifier.isAbstract(aspectClass.getSuperclass().getModifiers())) {
+		Class<?> superclass = aspectClass.getSuperclass();
+		if (superclass.getAnnotation(Aspect.class) != null &&
+				!Modifier.isAbstract(superclass.getModifiers())) {
 			throw new AopConfigException("[" + aspectClass.getName() + "] cannot extend concrete aspect [" +
-					aspectClass.getSuperclass().getName() + "]");
+					superclass.getName() + "]");
 		}
 
 		AjType<?> ajType = AjTypeSystem.getAjType(aspectClass);