null values in castor unmarshalling

[maya fur]

Hi,
I'm using castor to unmarshall xml to java objects. The only problem is that I'm not able to get null values...
In the xsd the element is nillable
<xs:element name="OC" type="xs ouble" nillable="true"/>
and in the castor mapping file I defined the type as object, not a primitive
<field name="OC" type="java.lang.Double" required="false" direct="false" transient="false">
<bind-xml name="OC" node="element" reference="false"/>
</field>
In addition, I validate using the schema to unmarshal.setValidation("true");

If my xml does not have a tag, then this is field is null. But if the tag is empty (<OC></OC> then I get a Double with value 0.
Any idea how I can get null if the tag is sent?
Thanks