class_docstr: Not sure if I can avoid the state machine here
code: def _get_wom_rule(self) -> str | None:
      weekdays = unique(self.index.weekday)
      if len(weekdays) > 1:
          return None
  
      week_of_months = unique((self.index.day - 1) // 7)
      # Only attempt to infer up to WOM-4. See #9425
      week_of_months = week_of_months[week_of_months < 4]
      if len(week_of_months) == 0 or len(week_of_months) > 1:
          return None
  
      # get which week
      week = week_of_months[0] + 1
      wd = int_to_weekday[weekdays[0]]
  
      return f"WOM-{week}{wd}"
  
imports: from __future__ import annotations
  from typing import TYPE_CHECKING
  import numpy
  from pandas._libs import lib
  from pandas._libs.algos import unique_deltas
  from pandas._libs.tslibs import Timestamp, get_unit_from_dtype, periods_per_day, tz_convert_from_utc
  from pandas._libs.tslibs.ccalendar import DAYS, MONTH_ALIASES, MONTH_NUMBERS, MONTHS, int_to_weekday
  from pandas._libs.tslibs.dtypes import OFFSET_TO_PERIOD_FREQSTR, freq_to_period_freqstr
  from pandas._libs.tslibs.fields import build_field_sarray, month_position_check
  from pandas._libs.tslibs.offsets import DateOffset, Day, to_offset
  from pandas._libs.tslibs.parsing import get_rule_month
  from pandas.util._decorators import cache_readonly
  from pandas.core.dtypes.common import is_numeric_dtype
  from pandas.core.dtypes.dtypes import DatetimeTZDtype, PeriodDtype
  from pandas.core.dtypes.generic import ABCIndex, ABCSeries
  from pandas.core.algorithms import unique
label_desc: Use image node_id 20 for calling the _FrequencyInferer obj's underlying member method code with example usage: obj._get_wom_rule() and returns: str, week, wd, None, None