Bulding custom SOAP Header Handler in WM 7.1.2

Has anybody tried to create the custom SOAP header handlers in WM 7.1.2? I am trying to create one to set few fields in the inbound soap message body. So far I created only a skeleton header class implementing [SIZE=2]
javax.xml.rpc.handler.Handler. I just implemented the required methods, doing really nothing inside, just a system.out.println statement. I am able to register this Handler and add to the WS Descriptor service too. But when I send SOAP message to the server it is throwing NullPointerException. The server log shows only following message

SOAPException: [ISS.0088.9112] An Exception was thrown in the server:null.

Any idea why that may be?

we have tried to add the Header in Soap Message. We are unable to handle the Header. We are trying for the custom soap handler.The reason is we are providing the username & Password dynamically in the Header. In this case we are the consumer. I got the following exception…

Soap Exception :- com.ibm.wsspi.wssecurity.SoapSecurityException: WSEC5509E: A security token whose type is [http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-username-token-profile-1.0#UsernameToken] is required.

We followed the steps as in the sample package WmServicUserHandler, but still we are not able to handle the Header.Any help will be appreciated .