NullPointerException If do not set the "Request Initializer"

[wuhelong]

@Override
public AuthorizationCodeTokenRequest newTokenRequest(String authorizationCode) {
    return new LenientAuthorizationCodeTokenRequest(getTransport(), getJsonFactory(),
            new GenericUrl(getTokenServerEncodedUrl()), authorizationCode)
            .setClientAuthentication(getClientAuthentication())
            .setScopes(getScopes())
            .setRequestInitializer(
                    new HttpRequestInitializer() {
                        @Override
                        public void initialize(HttpRequest request) throws IOException {
                             //NullPointerException If do not set the "Request Initializer"
                            getRequestInitializer().initialize(request);
                            request.getHeaders().setAccept("application/json");
                        }
                    });
}