StandardImplForwardingMap<String, String> forwardingMap =
        new StandardImplForwardingMap<>(Maps.<String, String>newHashMap());
    forwardingMap.put("foo", "bar");
    forwardingMap.put("baz", null);

    assertEquals(hashmap.toString(), forwardingMap.toString());
  }

  private static <K, V> Map<K, V> wrap(final Map<K, V> delegate) {
    return new ForwardingMap<K, V>() {
      @Override

    StandardImplForwardingMap<String, String> forwardingMap =
        new StandardImplForwardingMap<>(Maps.<String, String>newHashMap());
    forwardingMap.put("foo", "bar");
    forwardingMap.put("baz", null);

    assertEquals(hashmap.toString(), forwardingMap.toString());
  }

  private static <K, V> Map<K, V> wrap(final Map<K, V> delegate) {
    return new ForwardingMap<K, V>() {
      @Override