def METHOD_NAME():
    df = pd.DataFrame(
        {
            "string_object": ["a", "b", "c", "d"],
            "string_string": pd.array(["a", "b", "c", "d"], dtype="string"),
            "string_object_null": ["a", "b", None, "d"],
            "string_string_null": pd.array(["a", "b", None, "d"], dtype="string"),
        }
    )
    df_clean = sanitize_dataframe(df)
    assert {col.dtype.name for _, col in df_clean.items()} == {"object"}
    result_python = {col_name: list(col) for col_name, col in df_clean.items()}
    assert result_python == {
        "string_object": ["a", "b", "c", "d"],
        "string_string": ["a", "b", "c", "d"],
        "string_object_null": ["a", "b", None, "d"],
        "string_string_null": ["a", "b", None, "d"],
    }