* should not be possible to access the raw (modifiable) map entry via a nefarious equals method.
   */
  public static <K extends @Nullable Object, V extends @Nullable Object>
      Entry<K, V> nefariousMapEntry(K key, V value) {
    return new Entry<K, V>() {
      @Override
      public K getKey() {
        return key;
      }

      @Override
      public V getValue() {
        return value;