docs: private Set<String> versionLabelsFor( Version version ) throws RepositoryException {
          if (!version.getParent().equals(this)) {
              throw new VersionException(JcrI18n.invalidVersion.text(version.getPath(), getPath()));
          }
  
          String versionId = version.getIdentifier();
          PropertyIterator iter = versionLabels().getProperties();
          if (iter.getSize() == 0) return Collections.emptySet();
  
          Set<String> labels = new HashSet<String>();
          while (iter.hasNext()) {
              javax.jcr.Property prop = iter.nextProperty();
              if (versionId.equals(prop.getString())) {
                  labels.add(prop.getName());
              }
          }
          return labels;
      }