Session attribute as method argument with Spring MVC

I'm using Bozho solution to create a session attribute annotation under Spring mvc.

I've a problem when the object is not in the session and I've something like

@SessionAttribute(required = false) MyFormObject myFormObject

The annotation is defined as

@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface SessionAttribute {
    String value() default "";
    boolean required() default true;
    String defaultValue() default ValueConstants.DEFAULT_NONE;
}

I get an exception since defaultValue() returns a String and my custom ArgumentResolver tries to assign this String to MyFormObject.

How can I instruct Spring to assign 开发者_StackOverflow中文版null to myFormObject instead of ValueConstants.DEFAULT_NONE?

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Can't you simple modify the custom WebArgumentResolver to return null instead of defaultValue when attribute is not found?

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the defaultValue can be the username of the user, which you can find by injecting a dao into the resolver. But having a default user doesn't make much sense anyway, so just return null