code: def backward(self):
      if isinstance(self._agg_layer, SSHEAggLayerHost):
          self._fake_loss.backward()
          self._fake_loss = None
          self._agg_layer.step()  # sshe has independent optimizer
          self._clear_state()
      else:
          error = self._agg_layer.backward()
          error = error.to(self.device)
          loss = backward_loss(self._bottom_fw, error)
          loss.backward()
          self._clear_state()
  
imports: import torch
  import torch
  from fate.arch import Context
  from fate.ml.nn.model_zoo.agg_layer.agg_layer import AggLayerGuest, AggLayerHost
  from fate.ml.nn.model_zoo.agg_layer.fedpass.agg_layer import FedPassAggLayerGuest, FedPassAggLayerHost, get_model
  from fate.ml.nn.model_zoo.agg_layer.sshe.agg_layer import SSHEAggLayerHost, SSHEAggLayerGuest
  from typing import Any, Dict, List, Union, Callable, Literal
  from dataclasses import dataclass, fields
  from enum import Enum
  import logging
  from torch import device
label_desc: Use image node_id 8 for calling the HeteroNNModelHost obj's underlying member method code with example usage: obj.backward() without return types