How do I get Robospice to treat anything other than a 200 response from Retrofit & OKHttp as an error-open source projects square/okhttp

I am using Robospice on android with Retrofit and OKHttp. All works great with responses passed back to the activity using the Robospice RequestListener. The problem is that it only returns a failure if the connection times out or another network issue. If a 401 is returned then it is classed as a success but with a null response as it couldn’t parse the JSON into our MobileAppSetup POJO.

At the moment I’m having to do null checking on the response but I have no idea what the reason was if it was a server error or a valid 401.

public final class HTTPRequestListener implements RequestListener {

    @Override
    public void onRequestFailure(SpiceException spiceException) {
        Log.d("", "failure:"+ spiceException);
        loginProgress.hide();

    }

    @Override
    public void onRequestSuccess(final MobileAppSetup response) {
        Log.d("","success. Data: "+response);

        if(response==null)
            showDialog("Error logging in", "Please check your username and password and try again.", "");

        loginProgress.hide();

        postLoginProcess(response);

    }
} 

I need to pass these errors to the onRequestFailure callback so I can properly handle it. Is there a way to specify error codes that Robospice should treat as an error. I think it involves adding some kind of custom error handler but really can’t find a solution at the moment.