code: def test_margin_dropna5(self):
      # GH: 10772: Keep np.nan in result with dropna=False
      df = DataFrame(
          {
              "a": [1, np.nan, np.nan, np.nan, 2, np.nan],
              "b": [3, np.nan, 4, 4, 4, 4],
          }
      )
      actual = crosstab(df.a, df.b, margins=True, dropna=False)
      expected = DataFrame(
          [
              [1, 0, 0, 1.0],
              [0, 1, 0, 1.0],
              [0, 3, 1, np.nan],
              [1, 4, 0, 6.0],
          ]
      )
      expected.index = Index([1.0, 2.0, np.nan, "All"], name="a")
      expected.columns = Index([3.0, 4.0, np.nan, "All"], name="b")
      tm.assert_frame_equal(actual, expected)
  
imports: import numpy
  import pytest
  import pandas
  from pandas import CategoricalDtype, CategoricalIndex, DataFrame, Index, MultiIndex, Series, crosstab
  import pandas._testing
label_desc: Use image node_id 14 for calling the TestCrosstab obj's underlying member method code with example usage: obj.test_margin_dropna5() without return types