code: def test_assign_null(
      self, hydra_restore_singletons: Any, path: str
  ) -> None:
      config_loader = ConfigLoaderImpl(
          config_search_path=create_config_search_path(path)
      )
      cfg = config_loader.load_configuration(
          config_name="config.yaml",
          overrides=["+abc=null"],
          run_mode=RunMode.RUN,
      )
      with open_dict(cfg):
          del cfg["hydra"]
      assert cfg == {"normal_yaml_config": True, "abc": None}
  
imports: import re
  from dataclasses import dataclass, field
  from textwrap import dedent
  from typing import Any, List
  from omegaconf import MISSING, OmegaConf, ValidationError, open_dict
  from pytest import mark, param, raises, warns
  from hydra import version
  from hydra._internal.config_loader_impl import ConfigLoaderImpl
  from hydra._internal.utils import create_config_search_path
  from hydra.core.config_store import ConfigStore, ConfigStoreWithProvider
  from hydra.core.override_parser.overrides_parser import OverridesParser
  from hydra.core.utils import env_override, setup_globals
  from hydra.errors import ConfigCompositionException, HydraException, MissingConfigException
  from hydra.test_utils.test_utils import chdir_hydra_root
  from hydra.types import RunMode
  from tests.instantiate import UserGroup
label_desc: Use image node_id 16 for calling the TestConfigLoader obj's underlying member method code with example usage: obj.test_assign_null(hydra_restore_singletons, path) without return types