org.hibernate.internal.util.config.ConfigurationException: Unable to perform unmarshalling at line number 0 and column 0 in RESOURCE hibernate.cfg.xml. Message: null

am using Hibernate-core-jakarata:5.6.15.FInal now . And also we have hibernate.cfg.xml and hbm.xml files .
Session creation as below …--------------
public static Session currentSession(String instance) throws
HibernateException {

	log.finest("currentSession called for " + instance +
			" [" + Thread.currentThread().getName() + "]");

	// Check if the thread local object is registered with the instance
	ThreadLocal tl = null;
	synchronized (sessionFactoryLock) {
		tl = (ThreadLocal) sessionPerThreadMap.get(instance);
		if (tl == null) {
			log.finest("Session not found for instance " + instance +
					" [" + Thread.currentThread().getName() + "]");
			// Check if the session factory is created. If not, initialise it
			SessionFactory factory = (SessionFactory) sessionFactoryMap.get(
					instance);
			if (factory == null) {
				log.finest("Session factory not found for instance " + instance);
				HibernateUtil.initFactory(instance);
			}

			tl = (ThreadLocal) sessionPerThreadMap.get(instance);
		}
	}

	Session s = (Session) tl.get();
	// Open a new Session, if this Thread has none yet
	if (s == null) {
		log.finest("Opening new session for instance " + instance +
				" [" + Thread.currentThread().getName() + "]");
        s = ((SessionFactory) sessionFactoryMap.get(instance)).openSession();
		((ThreadLocal) sessionPerThreadMap.get(instance)).set(s);
	}
	return s;
}

------session factory creation –
Configuration cfg = new Configuration();

        //Read in the defaults from persistence.jar
		cfg.configure(HibernateUtil.class.getResource("/hibernate.cfg.xml"));

        //Read in list of persistable POJOs
		cfg.configure("/hibernate_" + instance + ".cfg.xml");

		if(!useDataSource(cfg)) {
			// Name for connectionpool
			cfg.setProperty(HibernateConnectionProvider.POOL_ID_PROPERTY_NAME,
					instance);

			// Resolve database name used in DB_INFO_FILE
			String dbName = resolveDatabaseName(cfg, instance);

			// Read connection information from DB_INFO_FILE and set
			// Hibernate configration parameters
			if ((dbinfo != null) && (dbinfo.getProperties(dbName) != null)) {
				configureDBInfo(cfg, dbName);
			}
			else {
				log.info("Database connection information not set in the " +
						"DB_INFO_FILE for " + dbName + ". Expecting " +
				"information to be found from Hibernate configuration");
			}
		}

		log.info("Calling Hibernate configuration listeners for " + instance + " ...");
		cfg = callConfigurationListeners(cfg, instance);

        log.info("Building Hinernate session factory for " + instance + " ...");
		// create session factory
		SessionFactory sf = cfg.buildSessionFactory();

		// add session factory to a map
		sessionFactoryMap.put(instance, sf);

		// add ThreadLocal to a session map
		sessionPerThreadMap.put(instance, new ThreadLocal());

		return sf;