JaxB2Marshaller throwing Null pointer Exception

Question

So, I have this method which marshals an object.

public String marshalResponse(Object messageObject) {
    if (messageObject == null) {
        return null;
    }
    String finalstring ="No results found!";
    try {

        StringWriter sw = new StringWriter();
        StreamResult streamResult = new StreamResult(sw);
        getJaxb2Marshaller().marshal(messageObject, streamResult);
        StringWriter sw2 = (StringWriter) streamResult.getWriter();
        StringBuffer sb = sw2.getBuffer();
        finalstring = sb.toString();
        System.out.println("Response:"+finalstring);
        return finalstring;
    } catch (Exception ex) {
        log.warn("marshalObject(): Exception caught while trying to marshal an object (object.class.name="
                + messageObject.getClass().getName() + ", ex=" + ex + ")");

    }
    return null;
}

getJaxb2Marshaller()

    public Jaxb2Marshaller getJaxb2Marshaller() {
    return jaxb2Marshaller;
}

I dont know why it is throwing null pointer exception at getJaxb2Marshaller().marshal(messageObject, sw); And Over that, when I tried to sysout the finalstring, it is giving a legimitate output but the method itself is returning Null. I put a debug on code and found, the null pointer is because of StreamResult which is null. I have no idea, why it is coming like that. Please help!