}

  // Logically this would accept a NavigableMap, but that won't work under GWT.
  private static <K, V> SortedMap<K, V> sortedNotNavigable(SortedMap<K, V> map) {
    return new ForwardingSortedMap<K, V>() {
      @Override
      protected SortedMap<K, V> delegate() {
        return map;
      }
    };
  }

  public void testSortedMapTransformValues() {

  }

  @GwtIncompatible // NavigableMap
  private static final class UnmodifiableNavigableMap<
          K extends @Nullable Object, V extends @Nullable Object>
      extends ForwardingSortedMap<K, V> implements NavigableMap<K, V>, Serializable {
    private final NavigableMap<K, ? extends V> delegate;

    UnmodifiableNavigableMap(NavigableMap<K, ? extends V> delegate) {
      this.delegate = delegate;

  }

  @GwtIncompatible // NavigableMap
  private static final class UnmodifiableNavigableMap<
          K extends @Nullable Object, V extends @Nullable Object>
      extends ForwardingSortedMap<K, V> implements NavigableMap<K, V>, Serializable {
    private final NavigableMap<K, ? extends V> delegate;

    UnmodifiableNavigableMap(NavigableMap<K, ? extends V> delegate) {
      this.delegate = delegate;