code: private static String convertConnection(String notation, String source, String target, Map<String, String> convertIds) throws HELM1ConverterException {
      try {
        String test = notation.replace(source, "one");
        test = test.replace(target, "two");
        test = test.replace("one", convertIds.get(source));
        test = test.replace("two", convertIds.get(target));
        return test;
      } catch (NullPointerException ex) {
        ex.printStackTrace();
        LOG.error("Connection can't be downgraded to HELM1-Format");
        throw new HELM1ConverterException("Connection can't be downgraded to HELM1-Format");
      }
    }
docs: method to convert the polymers ids of the connection
  
  @param notation connection description in HELM
  @param source polymer id of source
  @param target polymer id of target
  @param convertIds Map of old polymer ids with the new polymer ids
  @return connection description in HELM with the changed polymer ids
  according to the map
  @throws HELM1ConverterException