@Override
        void fire(final MutationListener listener, final Element element, final Property oldValue, final Object newValue, final Object... vertexPropertyKeyValues) {
            listener.vertexPropertyChanged((Vertex) element, (VertexProperty) oldValue, newValue, vertexPropertyKeyValues);
        }
Represents an action where a {@link VertexProperty} is modified on a {@link Vertex}. If the {@link Property} is
new then the {@code oldValue} will be {@code null}.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/event/Event.java