Expression detection properly handles cached String literals

Issue: SPR-9670

spring-beans/src/main/java/org/springframework/beans/factory/support/BeanDefinitionValueResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2010 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -38,6 +38,7 @@ import org.springframework.beans.factory.config.RuntimeBeanNameReference;
 import org.springframework.beans.factory.config.RuntimeBeanReference;
 import org.springframework.beans.factory.config.TypedStringValue;
 import org.springframework.util.ClassUtils;
+import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 
 /**
@@ -208,7 +209,7 @@ class BeanDefinitionValueResolver {
 	 */
 	protected Object evaluate(TypedStringValue value) {
 		Object result = this.beanFactory.evaluateBeanDefinitionString(value.getValue(), this.beanDefinition);
-		if (result != value.getValue()) {
+		if (!ObjectUtils.nullSafeEquals(result, value.getValue())) {
 			value.setDynamic();
 		}
 		return result;