code: def test_dump_nothing():
      """Ensure that by default None objects are dumped."""
      with tempfile.NamedTemporaryFile() as tmp_file:
          dump.dump(tmp_file.name)
          predictions, algo = dump.load(tmp_file.name)
          assert predictions is None
          assert algo is None
  
imports: import random
  import tempfile
  import pytest
  from surprise import BaselineOnly, CoClustering, dump, KNNBaseline, KNNBasic, KNNWithMeans, KNNWithZScore, NMF, NormalPredictor, SlopeOne, SVD, SVDpp
  from surprise.model_selection import PredefinedKFold
label_desc: Use image node_id 2 for calling a global function with example usage: test_dump_nothing() without return types