code: def test_infer_problem_type_multiclass_with_nan(self):
      inferred_problem_type = infer_problem_type(
          pd.Series(["a", "b", "c", np.nan])
      )
      assert inferred_problem_type == MULTICLASS
  
imports: import unittest
  import numpy
  import pandas
  import pytest
  from autogluon.core.constants import BINARY, MULTICLASS, MULTICLASS_UPPER_LIMIT, REGRESSION
  from autogluon.core.utils import infer_problem_type
  from autogluon.core.utils.utils import generate_train_test_split
label_desc: Use image node_id 10 for calling the TestInferProblemType obj's underlying member method code with example usage: obj.test_infer_problem_type_multiclass_with_nan() without return types