code: def preprocess_session(self, session_id, args):
      if session_id not in self.session_context:
          raise ValueError(f"session {session_id} does not exist")
      if self.session_context[session_id] is None:
          self.session_context[session_id] = ""
      if len(args[0]) != 1:
          raise ValueError(
              f"You can pass only one prompt with a session_id"
          )
  
      args = ([self.session_context[session_id] + args[0][0]],)
      return args
  
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 4 for calling the TextGenerationMethods obj's underlying member method code with example usage: obj.preprocess_session(session_id, args) and returns: args