NPE when configuring externalizers via XML

java.lang.NullPointerException
	at org.infinispan.configuration.global.SerializationConfigurationBuilder.addAdvancedExternalizer(SerializationConfigurationBuilder.java:83)
	at org.infinispan.configuration.global.LegacyGlobalConfigurationAdaptor.adapt(LegacyGlobalConfigurationAdaptor.java:113)
	at org.infinispan.manager.DefaultCacheManager.getCacheManagerConfiguration(DefaultCacheManager.java:761)
	at org.infinispan.configuration.XmlFileParsingTest.assertNamedCacheFile(XmlFileParsingTest.java:90)
	at org.infinispan.configuration.XmlFileParsingTest.testNamedCacheFile(XmlFileParsingTest.java:86)