code: def _get_target_reward(self, batch: rlt.PreprocessedRankingInput):
      if isinstance(batch, rlt.PreprocessedRankingInput):
          target_reward = batch.slate_reward
      else:
          target_reward = batch.reward
      assert target_reward is not None
      return target_reward
  
imports: import logging
  from enum import Enum
  from typing import Optional
  import numpy
  import reagent.core.types
  import torch
  from reagent.core.dataclasses import field
  from reagent.models.base import ModelBase
  from reagent.optimizer.union import Optimizer__Union
  from reagent.training.reagent_lightning_module import ReAgentLightningModule
label_desc: Use image node_id 4 for calling the RewardNetTrainer obj's underlying member method code with example usage: obj._get_target_reward(batch) and returns: target_reward