code: public static String getNaturalAnalogSequence(PolymerNotation polymer)
  			throws HELM2HandledException, RNAUtilsException, ChemistryException {
  		checkRNA(polymer);
  		return FastaFormat
  				.generateFastaFromRNA(MethodsMonomerUtils.getListOfHandledMonomers(polymer.getPolymerElements().getListOfElements()));
  	}
docs: method to generate the natural analogue sequence of a rna/dna of a given
  polymer
  
  @param polymer
  PolymerNotation
  @return sequence natural analogue sequence
  @throws HELM2HandledException
  if the polymer contains HELM2 features
  @throws RNAUtilsException
  if the polymer is not RNA or DNA
  @throws ChemistryException
  if the Chemistry Engine can not be initialized