code: public final static List<PolymerNotation> getRNAPolymers(List<PolymerNotation> polymers) {
      List<PolymerNotation> rnaPolymers = new ArrayList<PolymerNotation>();
      for (PolymerNotation polymer : polymers) {
        if (polymer.getPolymerID() instanceof RNAEntity) {
          rnaPolymers.add(polymer);
        }
      }
      return rnaPolymers;
    }
docs: method to get all rna polymers given a List of PolymerNotation objects
  
  @param polymers List of PolymerNotation
  @return list of rna polymers