code: def test_pure_null_column(self):
      batches = [
          pa.RecordBatch.from_arrays(
              [
                  pa.array([None, None], type=pa.null()),
                  pa.array([[1.0], [1.0]]),
              ],
              ["a", "w"],
          ),
          pa.RecordBatch.from_arrays(
              [
                  pa.array([None], type=pa.null()),
                  pa.array([[1.0]]),
              ],
              ["a", "w"],
          ),
      ]
      expected_result = {
          types.FeaturePath(["a"]): text_format.Parse(
              """
              type: STRING
              string_stats {
                common_stats {
                  num_missing: 3
                  weighted_common_stats {
                    num_missing: 3.0
                  }
                }
              }
              path {
                step: "a"
              }
              """,
              statistics_pb2.FeatureNameStatistics(),
          ),
      }
      generator = basic_stats_generator.BasicStatsGenerator(
          example_weight_map=ExampleWeightMap(weight_feature="w"),
          num_values_histogram_buckets=4,
          num_histogram_buckets=3,
          num_quantiles_histogram_buckets=4,
      )
      self.assertCombinerOutputEqual(
          batches,
          generator,
          expected_result,
          only_match_expected_feature_stats=True,
      )
  
imports: from absl.testing import absltest
  from absl.testing import parameterized
  import numpy
  import pyarrow
  from tensorflow_data_validation import types
  from tensorflow_data_validation.statistics.generators import basic_stats_generator
  from tensorflow_data_validation.utils import test_util
  from tensorflow_data_validation.utils.example_weight_map import ExampleWeightMap
  from google.protobuf import text_format
  from tensorflow_metadata.proto.v0 import schema_pb2
  from tensorflow_metadata.proto.v0 import statistics_pb2
label_desc: Use image node_id 8 for calling the BasicStatsGeneratorTest obj's underlying member method code with example usage: obj.test_pure_null_column() without return types