public static <K, V> MapCoder<K, V> of(Coder<K> keyCoder, Coder<V> valueCoder) {
    return new MapCoder<>(keyCoder, valueCoder);
  }
@Test
  public void testCoderIsSerializableWithWellKnownCoderType() throws Exception {
    CoderProperties.coderSerializable(
        MapCoder.of(GlobalWindow.Coder.INSTANCE, GlobalWindow.Coder.INSTANCE));
  }