code: def backward(self, error=None) -> t.Tensor:
      error = self._get_error_from_guest()
      if self._input_cache is not None and self._model is not None:
          error = error.to(self.device)
          loss = backward_loss(self._out_cache, error)
          loss.backward()
          error = self._input_cache.grad
          self._clear_state()
          return error
      else:
          return error
  
imports: import torch
  from typing import List, Literal
  import torch
  from fate.arch import Context
  from torch.nn.modules.module import T
label_desc: Use image node_id 6 for calling the AggLayerHost obj's underlying member method code with example usage: obj.backward(error) and returns: error, error