code: @Override
    public List<IScan> getScansByRtLower(double rt) {
      Map.Entry<Double, List<IScan>> lowerEntry = getRt2scan().lowerEntry(rt);
      if (lowerEntry == null) {
        return null;
      }
      List<IScan> scans = lowerEntry.getValue();
      if (scans != null) {
        return scans;
      }
      return null;
    }
docs: Scan List with closest RT less or equal to the provided one are returned.