code: @Override
    public List<IScan> getScansByRtClosest(double rt) {
      List<IScan> result = null;
      Map.Entry<Double, List<IScan>> lower = getMapRt2scan().lowerEntry(rt);
      Map.Entry<Double, List<IScan>> upper = getMapRt2scan().ceilingEntry(rt);
      if (upper != null && lower != null) {
        if (Math.abs(rt - lower.getKey()) <= Math.abs(rt - upper.getKey())) {
          result = lower.getValue();
        } else {
          result = upper.getValue();
        }
  //            result = Double.compare(lower.getKey(), upper.getKey()) > 0 ? lower.getValue() : upper.getValue();
      } else if (upper != null) {
        result = upper.getValue();
      } else if (lower != null) {
        result = lower.getValue();
      }
      return result;
    }
docs: Scans with the closest RT are returned.
  
  @return null if no scans were found at all, but this should only happen if your ScanCollection
  is empty.