code: def serialize(self, index_file: str):
      logger.info("Serializing index to %s", index_file)
      faiss.write_index(self.index, index_file)
  
imports: import os
  import logging
  import pickle
  import faiss
  import numpy
label_desc: Use image node_id 4 for calling the DenseIndexer obj's underlying member method code with example usage: obj.serialize(index_file) without return types