code: def test_inverse_transform_BothFieldsAreReturnNanWithNan_ExpectValueError(
      self,
  ):
      train = pd.DataFrame({"city": ["chicago", np.nan]})
      test = pd.DataFrame({"city": ["chicago", "los angeles"]})
  
      enc = encoders.OrdinalEncoder(
          handle_missing="return_nan", handle_unknown="return_nan"
      )
      enc.fit(train)
      result = enc.transform(test)
  
      message = (
          "inverse_transform is not supported because transform impute "
          "the unknown category nan when encode city"
      )
  
      with self.assertWarns(UserWarning, msg=message) as w:
          enc.inverse_transform(result)
  
imports: import pandas
  from unittest import TestCase
  import tests.helpers
  import numpy
  import category_encoders
label_desc: Use image node_id 17 for calling the TestOrdinalEncoder obj's underlying member method code with example usage: obj.test_inverse_transform_BothFieldsAreReturnNanWithNan_ExpectValueError() without return types