Application using Hibernate sometimes have problem to deploy with NPE.

Issue

From the time to time, following error happen. Why this error occur?

2013-10-18 18:05:40,636 WARN   [org.hibernate.engine.jdbc.internal.JdbcServicesImpl] HHH000341: Could not obtain connection metadata : Closed Connection
2013-10-18 18:05:40,642 INFO   [org.hibernate.engine.jdbc.internal.LobCreatorBuilder]  HHH000422: Disabling contextual LOB creation as connection was null
2013-10-18 18:05:40,644 ERROR  [org.jboss.msc.service.fail]  MSC000001: Failed to start service jboss.persistenceunit."admintest.ear/admintest-dao-4.10-PPP.jar#adminReadonly": org.jboss.msc.service.StartException in service jboss.persistenceunit."admintest.ear/admintest-dao-4.10-PPP.jar#adminReadonly": java.lang.NullPointerException
        at org.jboss.as.jpa.service.PersistenceUnitServiceImpl$1.run(PersistenceUnitServiceImpl.java:103)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:724)
        at org.jboss.threads.JBossThread.run(JBossThread.java:122)
Caused by: java.lang.NullPointerException
        at org.hibernate.engine.jdbc.internal.JdbcServicesImpl.configure(JdbcServicesImpl.java:207)