code: def test_null_csv_format():
      """test_null_csv_format"""
      # cat tests/test_csv/null.csv
      # C1,C2,C3
      # 1,2,3
      # 4,NaN,6
      # 7,8,9
      csv_path = os.path.join(
          os.path.dirname(os.path.abspath(__file__)),
          "test_csv",
          "null.csv",
      )
      csv = tfio.IOTensor.from_csv(csv_path)
      assert np.all(
          csv.isnull("C2").to_tensor().numpy() == [False, True, False]
      )
  
file_path: io/tests/test_csv.py
imports: import os
  import tempfile
  import numpy
  import pandas
  import tensorflow_io
label_desc: Use image node_id 2 for calling a global function with example usage: test_null_csv_format() without return types