code: public static String getModifiedNucleotideSequence(PolymerNotation polymer)
  			throws RNAUtilsException, HELM2HandledException, ChemistryException {
  		checkRNA(polymer);
  		List<Nucleotide> nucleotides = getNucleotideList(polymer);
  		StringBuilder sb = new StringBuilder();
  		for (Nucleotide nucleotide : nucleotides) {
  			sb.append(nucleotide.getSymbol());
  		}
  		return sb.toString();
  
  	}
docs: method to get the modifiedNucleotideSequence of the given PolymerNotation
  
  @param polymer
  PolymerNotation
  @return modified nucleotide sequence
  @throws RNAUtilsException if the polymer is not a RNA/DNA
  @throws HELM2HandledException if it contains HELM2 specific features, it can not be casted to HELM1Format
  @throws ChemistryException if the chemistry engine can not be initialized