code: def get_trace_id_from_flask():
      
      if flask is None or not flask.request:
          return None
  
      header = flask.request.headers.get(_FLASK_TRACE_HEADER)
  
      if header is None:
          return None
  
      trace_id = header.split("/", 1)[0]
  
      return trace_id
docs: Get trace_id from flask request headers.
  
      :rtype: str
      :returns: TraceID in HTTP request headers.