code: def test_nan(self):
      x = pd.Series(
          [
              np.nan,
              "",
              "This IS a STRING.",
          ],
          dtype="string",
      )
      primitive_func = self.primitive().get_function()
      answers = pd.Series([pd.NA, 0, 2], dtype="Int64")
      pd.testing.assert_series_equal(
          primitive_func(x).astype("Int64"),
          answers,
          check_names=False,
      )
  
imports: import numpy
  import pandas
  from featuretools.primitives import UpperCaseWordCount
label_desc: Use image node_id 2 for calling the TestUpperCaseWordCount obj's underlying member method code with example usage: obj.test_nan() without return types