@Override
    public <S> BinaryOperator<S> getSackMerger() {
        return this.sideEffects.getSackMerger();
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/traversal/MemoryTraversalSideEffects.java