code: def null_db_instances():
      """Nullify singleton instance so that we can assure independent instantiation tests."""
      storage_factory.instance = None
      database_factory.instance = None
  
imports: from __future__ import annotations
  import getpass
  import os
  from typing import Any
  import numpy
  import pytest
  import yaml
  from pymongo import MongoClient
  import orion.core
  import orion.core.utils.backward
  from orion.algo.base import BaseAlgorithm
  from orion.algo.space import Space
  from orion.core.io import resolve_config
  from orion.core.io.database import database_factory
  from orion.core.utils import format_trials
  from orion.core.worker.trial import Trial
  from orion.storage.base import storage_factory
  from orion.testing import OrionState, mocked_datetime
label_desc: Use image node_id 14 for calling a global function with example usage: null_db_instances() without return types