}
  // TODO(b/166669239): This is needed to support AttrBuilder::Get for string
  // attributes. Number type attrs and DataType attrs work fine without this.
  // Consider getting rid of this and making the behavior between number types
  // and string consistent.
  forward_op_->attrs.BuildNodeDef();
  std::unique_ptr<GradientFunction> gradient_fn;

        support and new features.
    *   **API not found.** The new optimizer has a different set of public APIs
        from the old optimizer. These API changes are mostly related to
        getting rid of slot variables and TF1 support. Please check the API
        documentation to find alternatives to the missing API. If you must
        call the deprecated API, please change your optimizer to the legacy
        optimizer.