code: def test_isnull(self):
      pdf, psdf = self.array_pdf, self.array_psdf
      for col in self.array_df_cols:
          pser, psser = pdf[col], psdf[col]
          self.assert_eq(pser.isnull(), psser.isnull())
  
imports: import decimal
  import datetime
  import pandas
  from pyspark import pandas
  from pyspark.testing.pandasutils import PandasOnSparkTestCase
  from pyspark.pandas.tests.data_type_ops.testing_utils import OpsTestBase
label_desc: Use image node_id 33 for calling the ComplexOpsTestsMixin obj's underlying member method code with example usage: obj.test_isnull() without return types