code: @Override
    public boolean replace    ( TypeK  key, TypeV  oldValue, TypeV newValue ) {
      return Objects.equals(putIfMatch( key, newValue, oldValue ), oldValue);
    }
docs: Atomically do a <code>put(key,newValue)</code> if-and-only-if the key is
  mapped a value which is <code>equals</code> to <code>oldValue</code>.
  @throws NullPointerException if the specified key or value is null