@Override
        public Long generateFinalResult(final Iterator<KeyValue<MapReduce.NullObject, Long>> keyValues) {
            return keyValues.next().getValue();
        }
@author Marko A. Rodriguez (http://markorodriguez.com)
spark-gremlin/src/test/java/org/apache/tinkerpop/gremlin/spark/process/computer/CombineIteratorTest.java