code: def validation_step(self, batch, batch_idx):
      log_dict = self._validation_step(batch, batch_idx)
      with self.ema_scope():
          log_dict_ema = self._validation_step(
              batch, batch_idx, suffix="_ema"
          )
      return log_dict
  
imports: from contextlib import contextmanager
  import pytorch_lightning
  import torch
  import torch.nn.functional
  from nemo.collections.multimodal.modules.stable_diffusion.diffusionmodules.model import Decoder, Encoder
  from nemo.collections.multimodal.modules.stable_diffusion.distributions.distributions import DiagonalGaussianDistribution
  from nemo.collections.multimodal.parts.stable_diffusion.utils import instantiate_from_config
label_desc: Use image node_id 12 for calling the VQModel obj's underlying member method code with example usage: obj.validation_step(batch, batch_idx) and returns: log_dict