private void processNext() {
        final Tuple2<K, Iterable<V>> nextKeyValues = this.inputIterator.next();
        this.mapReduce.reduce(nextKeyValues._1(), nextKeyValues._2().iterator(), this.reduceIteratorEmitter);
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
spark-gremlin/src/main/java/org/apache/tinkerpop/gremlin/spark/process/computer/ReduceIterator.java