code: def test_12(self):
      nan = np.nan
      test_res = tools.nan_dot(self.mx_1, self.mx_2)
      expected_res = np.array([[nan, nan], [nan, nan]])
      assert_array_equal(test_res, expected_res)
  
imports: from statsmodels.compat.pandas import assert_frame_equal, assert_series_equal
  from statsmodels.compat.python import lrange
  import string
  import numpy
  from numpy.random import standard_normal
  from numpy.testing import assert_almost_equal, assert_array_equal, assert_equal, assert_string_equal
  import pandas
  import pytest
  from statsmodels.datasets import longley
  from statsmodels.tools import tools
  from statsmodels.tools.tools import pinv_extended
label_desc: Use image node_id 3 for calling the TestNanDot obj's underlying member method code with example usage: obj.test_12() without return types