code: def _email_to_hem(email: str) -> Optional[str]:
      if email is None or not isinstance(email, str) or email == "":
          return None
  
      if not EMAIL_REGEX.fullmatch(email):
          return None
  
      return sha256(email.lower().encode("utf-8")).hexdigest()
  
file_path: upgini/src/upgini/utils/email_utils.py
imports: import logging
  import re
  from hashlib import sha256
  from typing import Dict, List, Optional
  import pandas
  from pandas.api.types import is_string_dtype
  from upgini.resource_bundle import bundle
  from upgini.metadata import SearchKey
  from upgini.utils.base_search_key_detector import BaseSearchKeyDetector
label_desc: Use image node_id 2 for calling the EmailSearchKeyConverter obj's underlying member method code with example usage: obj._email_to_hem(email) and returns: sha256, None, None