code: public static AggregationIterator create(final List<Span> spans,
                                             final long start_time,
                                             final long end_time,
                                             final Aggregator aggregator,
                                             final Interpolation method,
                                             final Aggregator downsampler,
                                             final long sample_interval_ms,
                                             final boolean rate,
                                             final RateOptions rate_options) {
      return create(spans, start_time, end_time, aggregator, method, downsampler,
          sample_interval_ms, rate, rate_options, null);
    }
docs: Creates a new iterator for a {@link SpanGroup}.
  @param spans Spans in a group.
  @param start_time Any data point strictly before this timestamp will be
  ignored.
  @param end_time Any data point strictly after this timestamp will be
  ignored.
  @param aggregator The aggregation function to use.
  @param method Interpolation method to use when aggregating time series
  @param downsampler Aggregation function to use to group data points
  within an interval.
  @param sample_interval_ms Number of milliseconds wanted between each data
  point.
  @param rate If {@code true}, the rate of the series will be used instead
  of the actual values.
  @param rate_options Specifies the optional additional rate calculation
  options.
  @return An {@link AggregationIterator} object.