docs: ReadIteratorResource<Read, ReadGroupSet, Reference> queryNextInterval() {
      Stopwatch w = Stopwatch.createStarted();
      if (!isAtEnd()) {
        intervalIndex++;
      }
      if (isAtEnd()) {
        return null;
      }
      ReadIteratorResource<Read, ReadGroupSet, Reference> result =  
          queryForInterval(currentInterval());
      LOG.info("Interval query took: " + w);
      startTiming();
      return result;
    }