public PersonalEventList getPersonalEvents(String asUserId, String asLastModified) {
        if (asUserId == null || asUserId.trim().length() == 0) {
            throw new IllegalArgumentException("userId is null");
        }

        String lsParams = encode(asUserId);

        if (asLastModified != null && asLastModified.trim().length() > 0) {
            lsParams += "?last_modified=" + asLastModified;
        }
        return get(PersonalEventList.class, REST_URL_PERSONAL_EVENTS + lsParams);
    }