code: def test_highlight_null(styler):
      result = styler.highlight_null()._compute().ctx
      expected = {
          (1, 0): [("background-color", "red")],
          (1, 1): [("background-color", "red")],
      }
      assert result == expected
  
file_path: pandas/pandas/tests/io/formats/style/test_highlight.py
imports: import numpy
  import pytest
  from pandas import NA, DataFrame, IndexSlice
  from pandas.io.formats.style import Styler
label_desc: Use image node_id 3 for calling a global function with example usage: test_highlight_null(styler) without return types