src/main/java/org/helm/notation2/parser/notation/HELM2Notation.java
public PolymerNotation getSimplePolymer(String string) {
    for (PolymerNotation polymer : listOfPolymers) {
      if (polymer.getPolymerID().getId().equals(string)) {
        return polymer;
      }
    }
    return null;
  }
public PolymerNotation getSimplePolymer(String string) {
    for (PolymerNotation polymer : listOfPolymers) {
      if (polymer.getPolymerID().getId().equals(string)) {
        return polymer;
      }
    }
    return null;
  }
method to get the simple polymer type
@param string id of polymer
@return PolymerNotation with the given id