class_docstr: Represent an individual key/value pair at a given point in time.
  
  ConfigValue is immutable.
code: def new_version(self, session):
      raise NotImplementedError("ConfigValue is immutable.")
  
imports: from sqlalchemy import Column
  from sqlalchemy import create_engine
  from sqlalchemy import event
  from sqlalchemy import ForeignKey
  from sqlalchemy import Integer
  from sqlalchemy import String
  from sqlalchemy.ext.associationproxy import association_proxy
  from sqlalchemy.ext.declarative import declarative_base
  from sqlalchemy.orm import attributes
  from sqlalchemy.orm import backref
  from sqlalchemy.orm import make_transient
  from sqlalchemy.orm import relationship
  from sqlalchemy.orm import Session
  from sqlalchemy.orm import sessionmaker
  from sqlalchemy.orm import validates
  from sqlalchemy.orm.collections import attribute_keyed_dict
label_desc: Use image node_id 2 for calling the ConfigValue obj's underlying member method code with example usage: obj.new_version(session) without return types