code: def test_vstack_with_null_column() -> None:
      df1 = pl.DataFrame({"x": [3.5]}, schema={"x": pl.Float64})
      df2 = pl.DataFrame({"x": [None]}, schema={"x": pl.Null})
  
      result = df1.vstack(df2)
      expected = pl.DataFrame(
          {"x": [3.5, None]}, schema={"x": pl.Float64}
      )
  
      assert_frame_equal(result, expected)
  
      with pytest.raises(pl.SchemaError):
          df2.vstack(df1)
  
file_path: polars/py-polars/tests/unit/dataframe/test_vstack.py
imports: import pytest
  import polars
  from polars.testing import assert_frame_equal
label_desc: Use image node_id 9 for calling a global function with example usage: test_vstack_with_null_column() without return types