@Override
  public <K, T> UncommittedBundle<T> createKeyedBundle(
      StructuralKey<K> key, PCollection<T> output) {
    return UncommittedImmutableListBundle.create(output, key);
  }
@Test
  public void keyedWithNullKeyShouldCreateKeyedBundle() throws Exception {
    createKeyedBundle(VoidCoder.of(), null);
  }