We are getting a NullPointerException in clustered 2LC on EAP 6

Issue

We are currently using a Hibernate second-level cache for some of our object trees. We are seeing a case where we get an NPE in certain cases, and we are trying to nail down the root cause.

The payload validation errors in the hibernate_server.log file are due to the test we are running; both valid and invalid input are provided to the test, and all are handled as expected. The text to search for is "NullPointerException".

We do not use a persistence.xml file. I will attach standalone.xml - could you please let me know what other server configuration files you will need?

Here is the allowedValues declaration:

    /**
     * The set of allowed values for this configuration field.
     */
    @Cache(usage = CacheConcurrencyStrategy.TRANSACTIONAL)
    @ElementCollection(fetch = FetchType.EAGER)
    @CollectionTable(name = "nep_config_field_allowed_value", joinColumns = @JoinColumn(name = "field_id"))
    @Column(name = "allowed_value", length = ConfigurationFieldData.MAX_DEFAULT_VALUE_LENGTH, nullable = false)
    private Set<String> allowedValues = new HashSet<>();

This is used in the hashCode() implementation as follows:
    public int hashCode() {
        return new HashCodeBuilder().appendSuper(super.hashCode()).append(allowedValues).toHashCode();
    }

Stacktrace:

Caused by: java.lang.NullPointerException
        at org.hibernate.engine.internal.StatefulPersistenceContext.getLoadedCollectionOwnerOrNull(StatefulPersistenceContext.java:859) [hibernate-core-4.2.0.SP1-redhat-1.jar:4.2.0.SP1-redhat-1]
        at org.hibernate.event.spi.AbstractCollectionEvent.getLoadedOwnerOrNull(AbstractCollectionEvent.java:75) [hibernate-core-4.2.0.SP1-redhat-1.jar:4.2.0.SP1-redhat-1]
        at org.hibernate.event.spi.InitializeCollectionEvent.<init>(InitializeCollectionEvent.java:36) [hibernate-core-4.2.0.SP1-redhat-1.jar:4.2.0.SP1-redhat-1]
        at org.hibernate.internal.SessionImpl.initializeCollection(SessionImpl.java:1847) [hibernate-core-4.2.0.SP1-redhat-1.jar:4.2.0.SP1-redhat-1]
        at org.hibernate.collection.internal.AbstractPersistentCollection$4.doWork(AbstractPersistentCollection.java:549) [hibernate-core-4.2.0.SP1-redhat-1.jar:4.2.0.SP1-redhat-1]
        at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:234) [hibernate-core-4.2.0.SP1-redhat-1.jar:4.2.0.SP1-redhat-1]
        at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:545) [hibernate-core-4.2.0.SP1-redhat-1.jar:4.2.0.SP1-redhat-1]
        at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:124) [hibernate-core-4.2.0.SP1-redhat-1.jar:4.2.0.SP1-redhat-1]
        at org.hibernate.collection.internal.PersistentSet.hashCode(PersistentSet.java:428) [hibernate-core-4.2.0.SP1-redhat-1.jar:4.2.0.SP1-redhat-1]
        at org.apache.commons.lang3.builder.HashCodeBuilder.append(HashCodeBuilder.java:850) [commons-lang3-3.1.jar:3.1]
        at test.provisioning.configuration.domain.EnumConfigurationField.hashCode(EnumConfigurationField.java:122) [nep-provisioning-service-2.0.0-GA.jar:]
        at java.util.HashMap.hash(HashMap.java:366) [rt.jar:1.7.0_40]
        at java.util.HashMap.put(HashMap.java:496) [rt.jar:1.7.0_40]
...
        at org.hibernate.ejb.QueryImpl.getSingleResult(QueryImpl.java:283) [hibernate-entitymanager-4.2.0.SP1-redhat-1.jar:4.2.0.SP1-redhat-1]
        at org.springframework.data.jpa.repository.query.JpaQueryExecution$SingleEntityExecution.doExecute(JpaQueryExecution.java:123) [spring-data-jpa-1.2.0.RELEASE.jar:]
...