private Xpp3Dom convert(ReportPlugin plugin) {
        Xpp3Dom dom = new Xpp3Dom("reportPlugin", plugin.getLocation(""));

        addDom(dom, "groupId", plugin.getGroupId(), plugin.getLocation("groupId"));
        addDom(dom, "artifactId", plugin.getArtifactId(), plugin.getLocation("artifactId"));
        addDom(dom, "version", plugin.getVersion(), plugin.getLocation("version"));

        Xpp3Dom configuration = (Xpp3Dom) plugin.getConfiguration();

      @Override
      Entry<E> result(int entryIndex) {
        return backingMap.getEntry(entryIndex);
      }
    };
  }

  /** Allocation-free implementation of {@code target.addAll(this)}. */
  void addTo(Multiset<? super E> target) {
    checkNotNull(target);
    for (int i = backingMap.firstIndex(); i >= 0; i = backingMap.nextIndex(i)) {
      target.add(backingMap.getKey(i), backingMap.getValue(i));
    }
  }