code: public void sparsePrint(PrintStream stream) {
      if (mSeries.isEmpty()) {
        return;
      }
      long start = mSeries.firstKey();
      stream.printf("Time series starts at %d with width %d.%n", start, mWidthNano);
  
      for (Map.Entry<Long, Integer> entry : mSeries.entrySet()) {
        stream.printf("%d %d%n", (entry.getKey() - start) / mWidthNano, entry.getValue());
      }
    }
docs: Print the time series sparsely, i.e. it ignores buckets with 0 events.
  
  @param stream the print stream