code: @Override
    public IScan getScanByNum(int scanNum) {
      IScan scan = getNum2scan().get(scanNum);
      if (scan != null) {
        return scan;
      }
      return null;
    }
docs: The name says it all.
  
  @param scanNum Scan number as it was in the original MS file
  @return Scan or null, if no such scan number exists in this ScanCollection