code: private Map<String, Collection<String>> buildCommitGraph(List<Commit> commits) {
  		// multimap api doesn't quite fit what we want to do here
  		Map<String, Collection<String>> rt = new HashMap<>();
  		
  		// TODO build graph for svn
  		
  		for (Commit commit : commits) {
  			String revisionNumber = commit.getScmRevisionNumber();
  			boolean alreadyExists = false;
  			
  			List<String> parentRevisionNumbers = commit.getScmParentRevisionNumbers();
  			if (parentRevisionNumbers == null) {
  				alreadyExists = rt.put(revisionNumber, new ArrayList<>()) != null;
  			} else {
  				alreadyExists = rt.put(revisionNumber, parentRevisionNumbers) != null;
  			}
  			
  			if (alreadyExists) {
  				logger.warn("Error encountered building pipeline: multiple commits exist for revision number " + revisionNumber);
  			}
  		}
  		
  		return rt;
  	}
docs: We assume each commit belongs to the same repo + branch