code: def exog_missing_value_policy(
      self, mv: Union[MissingValuePolicy, str]
  ):
      if isinstance(mv, str):
          valid = set(MissingValuePolicy.__members__.keys())
          if mv not in valid:
              raise KeyError(
                  f"{mv} is not a valid missing value policy. Valid missing value policies are: {valid}"
              )
          mv = MissingValuePolicy[mv]
      self._exog_missing_value_policy = mv
  
imports: from abc import abstractmethod
  import copy
  import logging
  from typing import List, Optional, Tuple, Union
  import numpy
  import pandas
  from scipy.stats import norm
  from merlion.models.base import Config, ModelBase
  from merlion.plot import Figure
  from merlion.transform.base import TransformBase
  from merlion.transform.factory import TransformFactory
  from merlion.transform.normalize import MeanVarNormalize
  from merlion.utils.time_series import to_pd_datetime, to_timestamp, TimeSeries, AggregationPolicy, MissingValuePolicy
label_desc: Use image node_id 5 for calling the ForecasterExogConfig obj's underlying member method code with example usage: obj.exog_missing_value_policy(mv) without return types