*result = outputs[0];
  return absl::OkStatus();
}
}  // namespace

absl::Status GradientRegistry::Register(
    const string& op_name, GradientFunctionFactory gradient_function_factory) {
  auto iter = registry_.find(op_name);
  if (iter != registry_.end()) {
    return absl::AlreadyExistsError(
        absl::StrCat("Gradient already exists for op: ", op_name, "."));
  }