code: def test_first_order(self):
      # First order, so its Hessian will contain None
      params, y = self._generate_params_and_first_order_output()
  
      vec = torch.rand(4)
      # Hessian-vector product computation should raise an error
      with self.assertRaises(RuntimeError):
          compute_hessian_vector_product(y, params, vec)
  
imports: import os
  import tempfile
  import unittest
  import numpy
  import pytest
  import torch
  from torch import nn
  import pfrl
  from pfrl.agents import trpo
  from pfrl.envs.abc import ABC
  from pfrl.experiments import train_agent_batch_with_evaluation, train_agent_with_evaluation
  from pfrl.experiments.evaluator import batch_run_evaluation_episodes, run_evaluation_episodes
  from pfrl.nn import RecurrentSequential
  from pfrl.policies import GaussianHeadWithStateIndependentCovariance, SoftmaxCategoricalHead
  from pfrl.testing import torch_assert_allclose
label_desc: Use image node_id 3 for calling the TestHessianVectorProduct obj's underlying member method code with example usage: obj.test_first_order() without return types