code: def bilou_prefix_from_tag(tag: Text) -> Optional[Text]:
      """Returns the BILOU prefix from the given tag.
  
      Args:
          tag: the tag
  
      Returns: the BILOU prefix of the tag
      """
      if tag[:2] in BILOU_PREFIXES:
          return tag[:2]
      return None
  
imports: import logging
  import operator
  from collections import defaultdict, Counter
  from typing import List, Tuple, Text, Optional, Dict, Any, TYPE_CHECKING
  from rasa.nlu.constants import TOKENS_NAMES, BILOU_ENTITIES, BILOU_ENTITIES_GROUP, BILOU_ENTITIES_ROLE
  from rasa.shared.nlu.constants import TEXT, ENTITIES, ENTITY_ATTRIBUTE_START, ENTITY_ATTRIBUTE_END, ENTITY_ATTRIBUTE_TYPE, ENTITY_ATTRIBUTE_GROUP, ENTITY_ATTRIBUTE_ROLE, NO_ENTITY_TAG
label_desc: Use image node_id 1 for calling a global function with example usage: bilou_prefix_from_tag(tag) and returns: None, tag