@Override
    public ObjectWritable<A> value() {
        return this.value;
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
@author Stephen Mallette (http://stephen.genoprime.com)
spark-gremlin/src/main/java/org/apache/tinkerpop/gremlin/spark/process/computer/MemoryAccumulator.java