code: def default_reference(self, value):
      if not isinstance(value, ReferenceGenome):
          raise TypeError(
              f"{value} is {type(value)} not a ReferenceGenome"
          )
      self._default_ref = value
  
imports: from typing import Optional, Union, Tuple, Type, List, Dict
  from types import TracebackType
  import warnings
  import sys
  import os
  from contextlib import contextmanager
  from urllib.parse import urlparse, urlunparse
  from random import Random
  import pkg_resources
  from pyspark import SparkContext
  import hail
  from hail.genetics.reference_genome import ReferenceGenome, reference_genome_type
  from hail.typecheck import nullable, typecheck, typecheck_method, enumeration, dictof, oneof, sized_tupleof, sequenceof
  from hail.utils import get_env_or_default
  from hail.utils.java import Env, warning, choose_backend
  from hail.backend import Backend
  from hailtop.hail_event_loop import hail_event_loop
  from hailtop.utils import secret_alnum_string
  from hailtop.fs.fs import FS
  from hailtop.aiocloud.aiogoogle import GCSRequesterPaysConfiguration, get_gcs_requester_pays_configuration
  from .builtin_references import BUILTIN_REFERENCES
  from .backend.backend import local_jar_information
label_desc: Use image node_id 5 for calling the HailContext obj's underlying member method code with example usage: obj.default_reference(value) without return types