void createSessionFromId(long sessionId) {
        File sessionDir = getAndValidateExistingSessionAppDir(sessionId);
        ApplicationPackage applicationPackage = FilesApplicationPackage.fromFile(sessionDir);
        createLocalSession(sessionId, applicationPackage);
    }
Returns a new session instance for the given session id.
configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionRepository.java