code: def create_session(self, session_id):
      if session_id in self.session_context:
          raise ValueError(f"session {session_id} already exists")
      self.session_context[session_id] = None
  
imports: import uuid
  from abc import ABC, abstractmethod
  from transformers import Conversation
  from mii.legacy.constants import TaskType
  from mii.legacy.grpc_related.proto import legacymodelresponse_pb2
  from mii.legacy.utils import kwarg_dict_to_proto, unpack_proto_query_kwargs
  from mii.legacy.models.utils import ImageResponse
label_desc: Use image node_id 2 for calling the TextGenerationMethods obj's underlying member method code with example usage: obj.create_session(session_id) without return types