code: def test_null_preprocessing(direction: StudyDirection) -> None:
      trials_before = [
          create_trial(
              params={"x": 0.0},
              distributions={"x": FloatDistribution(-1, 1)},
              value=1.0,
          )
      ]
      p = _preprocessing.NullPreprocessing()
      trials_after = p.apply(trials_before, direction)
      assert trials_before == trials_after
  
file_path: optuna/tests/terminator_tests/improvement_tests/test_preprocessing.py
imports: from __future__ import annotations
  from unittest import mock
  import numpy
  import pytest
  from optuna.distributions import CategoricalDistribution
  from optuna.distributions import FloatDistribution
  from optuna.distributions import IntDistribution
  from optuna.study._study_direction import StudyDirection
  from optuna.terminator.improvement import _preprocessing
  from optuna.trial import create_trial
  from optuna.trial import FrozenTrial
label_desc: Use image node_id 3 for calling a global function with example usage: test_null_preprocessing(direction) without return types