code: def testEmptyComputeAndApplyApproximateVocabulary(self):
      input_data = [{"x": ""}] * 3
      input_metadata = tft.DatasetMetadata.from_feature_spec(
          {"x": tf.io.FixedLenFeature([], tf.string)}
      )
  
      def preprocessing_fn(inputs):
          index = (
              tft.experimental.compute_and_apply_approximate_vocabulary(
                  inputs["x"],
                  top_k=2,
                  file_format=self._VocabFormat(),
                  num_oov_buckets=1,
              )
          )
          return {"index": index}
  
      # We only filter empty tokens for `text` format.
      expected_data = [
          {"index": 1 if self._VocabFormat() == "text" else 0}
      ] * 3
      self.assertAnalyzeAndTransformResults(
          input_data, input_metadata, preprocessing_fn, expected_data
      )
  
imports: import os
  import apache_beam
  import tensorflow
  import tensorflow_transform
  from tensorflow_transform.beam import analyzer_impls
  from tensorflow_transform.beam import impl
  from tensorflow_transform.beam.tft_beam_io import transform_fn_io
  from tensorflow_transform.beam import tft_unit
  from tensorflow_metadata.proto.v0 import schema_pb2
label_desc: Use image node_id 6 for calling the VocabularyIntegrationTest obj's underlying member method code with example usage: obj.testEmptyComputeAndApplyApproximateVocabulary() and returns: dict