@Override
    public <V> void register(final String key, final Supplier<V> initialValue, final BinaryOperator<V> reducer) {
        this.sideEffects.register(key, initialValue, reducer);
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/traversal/MemoryTraversalSideEffects.java