@Override
    public void reduce(final ObjectWritable key, final Iterable<ObjectWritable> values, final Reducer<ObjectWritable, ObjectWritable, ObjectWritable, ObjectWritable>.Context context) throws IOException, InterruptedException {
        this.combineEmitter.setContext(context);
        this.mapReduce.combine(key.get(), IteratorUtils.map(values.iterator(), ObjectWritable::get), this.combineEmitter);
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
hadoop-gremlin/src/main/java/org/apache/tinkerpop/gremlin/hadoop/process/computer/HadoopCombine.java