code: def test_sum_empty_and_null_set() -> None:
      series = pl.Series("a", [], dtype=pl.Float32)
      assert series.sum() == 0
  
      series = pl.Series("a", [None], dtype=pl.Float32)
      assert series.sum() == 0
  
      df = pl.DataFrame(
          {"a": [None, None, None], "b": [1, 1, 1]},
          schema={"a": pl.Float32, "b": pl.Int64},
      )
      assert df.select(pl.sum("a")).item() == 0.0
      assert df.group_by("b").agg(pl.sum("a"))["a"].item() == 0.0
  
imports: from __future__ import annotations
  from datetime import date, datetime, timedelta
  from typing import TYPE_CHECKING, Any
  import numpy
  import pytest
  import polars
  from polars.testing import assert_frame_equal
label_desc: Use image node_id 18 for calling a global function with example usage: test_sum_empty_and_null_set() without return types