code: def add_unique_identity(session, uuid):
      
      if uuid is None:
          raise ValueError("'uuid' cannot be None")
      if uuid == '':
          raise ValueError("'uuid' cannot be an empty string")
  
      uidentity = UniqueIdentity(uuid=uuid)
      uidentity.profile = Profile()
      uidentity.last_modified = datetime.datetime.utcnow()
  
      session.add(uidentity)
  
      return uidentity
docs: Add a unique identity to the session.
  
      This function adds a unique identity to the session with
      `uuid` string as unique identifier. This identifier cannot
      be empty or `None`.
  
      When the unique identity is added, a new empty profile for
      this object is created too.
  
      As a result, the function returns a new `UniqueIdentity`
      object.
  
      :param session: database session
      :param uuid: unique identifier for the unique identity
  
      :return: a new unique identity
  
      :raises ValueError: when `uuid` is `None` or an empty string