"Class must exist and can not be null" error in webservice

Hi

I have exposed a webservice for BAPI_USER_GET_DETAIL and tried to consume it in WebDynpro but I am getting bellow error

Service call exception; nested exception is: com.sap.engine.services.webservices.jaxrpc.exceptions.XmlMarshalException: XML Serialization Error. Property [Return] of class [com.test_ws_usrgetdtl.usrgetdtl.models.usergetdetails.proxies.types.p1.UserGetDetail] must exist and can not be null. This is required by schema description.

Though I have instantiated the Return node in the custom controllers init method. Can any one help me out in this regards?

Thanks

Ninad