code: def validation_step(
      self, batch: rlt.BehavioralCloningModelInput, batch_idx: int
  ):
      self._check_input(batch)
      logits_masked = self._get_masked_logits(batch)
      labels = batch.action
      assert labels.ndim == logits_masked.ndim == 2
      assert labels.shape[0] == logits_masked.shape[0]
      _, integer_labels = labels.max(dim=0)
      loss = self.loss_fn(logits_masked, integer_labels)
      detached_loss = loss.detach().cpu()
      return detached_loss
  
file_path: ReAgent/reagent/training/behavioral_cloning_trainer.py
imports: import logging
  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 5 for calling the BehavioralCloningTrainer obj's underlying member method code with example usage: obj.validation_step(batch, batch_idx) and returns: detached_loss