code: private static List<Monomer> getMonomersRNAOnlyBase(MonomerNotationUnitRNA rna, MonomerStore monomerStore)
  			throws HELM2HandledException {
  		try {
  			List<Monomer> monomers = new ArrayList<Monomer>();
  			for (MonomerNotationUnit unit : rna.getContents()) {
  				String id = unit.getUnit().replace("[", "");
  				id = id.replace("]", "");
  				Monomer mon = MethodsMonomerUtils.getMonomer(rna.getType(), id, "");
  
  				if (mon.getMonomerType().equals(Monomer.BRANCH_MOMONER_TYPE)) {
  					monomers.add(mon);
  				}
  			}
  			return monomers;
  		} catch (Exception e) {
  			e.printStackTrace();
  			throw new HELM2HandledException(e.getMessage());
  		}
  
  	}
docs: method to get only the nucleotide base for one MonomerNotationUnitRNA
  
  @param rna
  MonomerNotationUnitRNA
  @param monomerStore
  MonomerStore
  @return List of Monomers
  @throws HELM2HandledException
  if HELM2 features were there