xjc binding file for <extension base = "anyType"/> throws error

Question

I have xsd defination

<element name="primaryKey" nillable="false">
   <complexType mixed="false">                   
      <complexContent mixed="false">
         <extension base="anyType"/>                   
      </complexContent>
   </complexType>
</element>

and i using binding file to

<jxb:bindings node="//xs:extension[@base='anyType']">
   <jxb:property>
      <jxb:baseType name="java.lang.Object"/>
   </jxb:property>
</jxb:bindings>

to generate the jaxb classes but i am unable to do so its giving error [xjc] [ERROR] Specified property customization is not used.