code: def test_null_grouping_12950() -> None:
      assert pl.DataFrame({"x": None}).unique().to_dict(
          as_series=False
      ) == {"x": [None]}
      assert pl.DataFrame({"x": [None, None]}).unique().to_dict(
          as_series=False
      ) == {"x": [None]}
      assert pl.DataFrame({"x": None}).slice(0, 0).unique().to_dict(
          as_series=False
      ) == {"x": []}
  
label_desc: Use image node_id 2 for calling a global function with example usage: test_null_grouping_12950() without return types