private void validateSessionStatus(Session session) {
        long sessionId = session.getSessionId();
        if (Session.Status.NEW.equals(session.getStatus())) {
            throw new IllegalArgumentException(session.logPre() + "Session " + sessionId + " is not prepared");
        } else if (Session.Status.ACTIVATE.equals(session.getStatus())) {
            throw new IllegalArgumentException(session.logPre() + "Session " + sessionId + " is already active");
        }
    }
@return config change actions that need to be performed as result of prepare
@throws IllegalArgumentException if called without being prepared by this
configserver/src/main/java/com/yahoo/vespa/config/server/deploy/Deployment.java