code: protected List<String> getCommitHistory(Map<String, Collection<String>> commitGraph, String headRevisionNumber) {
  		List<String> rt = new ArrayList<>();
  		Set<String> seenRevisions = new HashSet<>();
  		
  		seenRevisions.add(headRevisionNumber);
  		rt.add(headRevisionNumber);
  		getCommitHistory(rt, seenRevisions, commitGraph, headRevisionNumber);
  		
  		return rt;
  	}
docs: TODO need to handle SVN