Fix NPE in OAuth2TokenStore load method

    @Override
    public boolean load(String userName, Credential credential) {
        try {

            NuxeoOAuth2Token token = getToken(serviceName, userName);

            credential.setAccessToken(token.getAccessToken());
            credential.setRefreshToken(token.getRefreshToken());
            credential.setExpirationTimeMilliseconds(token.getExpirationTimeMilliseconds());
            return true;
        } catch (ClientException e) {
            log.error("Error during token loading", e);
            return false;
        }
    }