Due to an accidental reference to a Java 7 API (Collections#emptyIterator() in ValidatorImpl#createIteratorForCascadedValue() Hibernate Validator 5.1.2.Final is not compatible with Java 6. This should be changed to use e.g. emptyList().iterator() instead.
Apparently AnimalSniffer is not executed by default, otherwise we'd have caught that issue. This should be changed as well.