Avoid NPE in AutoProxyRegistrar when no attribute found

Issue: SPR-15055

Author: sdeleuze

spring-context/src/main/java/org/springframework/context/annotation/AutoProxyRegistrar.java

@@ -60,6 +60,9 @@ public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, B
 		Set<String> annoTypes = importingClassMetadata.getAnnotationTypes();
 		for (String annoType : annoTypes) {
 			AnnotationAttributes candidate = AnnotationConfigUtils.attributesFor(importingClassMetadata, annoType);
+			if (candidate == null) {
+				continue;
+			}
 			Object mode = candidate.get("mode");
 			Object proxyTargetClass = candidate.get("proxyTargetClass");
 			if (mode != null && proxyTargetClass != null && AdviceMode.class == mode.getClass() &&