These methods should return the map key but null is returned instead because the super constructor is not invoked correctly.

See discussion on infinispan dev list here: http://markmail.org/message/dkoughqngztmxvuy

This class could also be simplified a bit by removing the field deltaAwareValueKey which duplicates the key field of the base class.

Also since keys are non-null (asserted by constructor) the equals() and hashCode() methods can be simplified by removing the null checks.