How to generate unset methods in jaxb-2

I am migrating jaxb-1 to jaxb-2.1. Classes are generated using Metro-2.1.1 (XML Binding(JAXB) Reference Implementation, v2.2.4 ). With Global bindings setting :

<jaxb:globalBindings generateValueClass="false" generateIsSetMethod="true" >
<xjc:serializable uid="12343"/>
</jaxb:globalBindings>

Unset methods are generated only for elements with maxOccurs="unbounded"

please tell me how to generate unset methods for all elements (like in jaxb-1).

Thanks in advance.