@Override
        public void fireEvent(final Iterator<MutationListener> eventListeners) {
            while (eventListeners.hasNext()) {
                fire(eventListeners.next(), element, oldValue, newValue, vertexPropertyKeyValues);
            }
        }
A base class for {@link Property} mutation events.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/event/Event.java