public T getOrDefault(final T defaultValue) {
    return _delegate.getOrDefault(defaultValue);
  }
@Test
  public void testGetOrDefaultWithError() {
    final Promise<String> delegate = Promises.error(new Exception());
    final Promise<String> promise = new DelegatingPromise<String>(delegate);
    assertEquals(delegate.getOrDefault("defaultValue"), promise.getOrDefault("defaultValue"));
  }