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