code: def save_model(self, estimator):
      model = estimator.fit(self.get_data())
  
      # write model to file and validate it's there
      with tempfile.TemporaryDirectory() as tmpdirname:
          modelFile = "{}/model".format(tmpdirname)
  
          model.saveNativeModel(modelFile)
  
          self.assertTrue(os.stat(modelFile).st_size > 0)
  
imports: import os
  import unittest
  import tempfile
  import pyspark
  from synapsemltest.spark import *
  from synapse.ml.vw import VowpalWabbitContextualBandit
  from synapse.ml.vw import VowpalWabbitFeaturizer
  from synapse.ml.vw import VectorZipper
  from pyspark.ml.tuning import ParamGridBuilder
  from pyspark.sql.types import *
  from pyspark.ml import Pipeline
  from pyspark.ml.wrapper import *
  from pyspark.ml.common import inherit_doc, _java2py, _py2java
  from pyspark.sql.utils import AnalysisException
label_desc: Use image node_id 3 for calling the VowpalWabbitSpec obj's underlying member method code with example usage: obj.save_model(estimator) without return types