Message Title

I could reproduce it on my local (Linux) Workstation too, although it's apparently very rare:
Running org.hibernate.search.test.serialization.ConcurrentServiceTest
Tests run: 3, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 0.671 sec <<< FAILURE! - in org.hibernate.search.test.serialization.ConcurrentServiceTest
concurrentSerialization(org.hibernate.search.test.serialization.ConcurrentServiceTest)  Time elapsed: 0.223 sec  <<< FAILURE!
java.lang.AssertionError: null
	at org.junit.Assert.fail(Assert.java:86)
	at org.junit.Assert.assertTrue(Assert.java:41)
	at org.junit.Assert.assertFalse(Assert.java:64)
	at org.junit.Assert.assertFalse(Assert.java:74)
	at org.hibernate.search.testsupport.concurrency.ConcurrentRunner.execute(ConcurrentRunner.java:81)
	at org.hibernate.search.test.serialization.ConcurrentServiceTest.concurrentSerialization(ConcurrentServiceTest.java:51)

Running org.hibernate.search.test.serialization.ProtocolVersion10Test
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.013 sec - in org.hibernate.search.test.serialization.ProtocolVersion10Test
Running org.hibernate.search.test.serialization.SerializationTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.009 sec - in org.hibernate.search.test.serialization.SerializationTest

Results :

Failed tests: 
  ConcurrentServiceTest.concurrentSerialization:51 null