SOAP request returns code 404 after removing namespace from @PayloadRoot

Question

I am getting http code 404 after removing namespace field from @PayloadRoot where it was working when namespace was present there. Documentation says namespace is an optional field but after removing it its behavior is changed.

With namespace:

@PayloadRoot(namespace = NAMESPACE, localPart = "doSomething")
@ResponsePayload
public DoSomethingResponse update(@RequestPayload DoSomething doSomething) {
    return processRequest(doSomething);
}

Without namespace:

@PayloadRoot(localPart = "doSomething")
@ResponsePayload
public DoSomethingResponse update(@RequestPayload DoSomething doSomething) {
    return processRequest(doSomething);
}

I am new to this part and do not understand this behavior.

Is it possible to have the @PayloadRoot without namespace here ? as that is the current requirement.