code: def model_aggregation(self, *args, **kwargs):
      raise NotImplementedError(
          "model_aggregation should be implemented in subclass"
      )
  
imports: import logging
  from typing import Optional
  import numpy
  import torch
  from fate.arch import Context
  from fate.arch.protocol.secure_aggregation._secure_aggregation import SecureAggregatorClient
  from fate.arch.protocol.secure_aggregation._secure_aggregation import SecureAggregatorServer
label_desc: Use image node_id 2 for calling the Aggregator obj's underlying member method code with example usage: obj.model_aggregation() without return types