ProducesResponseType Type return for empty return

Question

What is the typeof return to indicate there is empty body return. For example 401 unauthorized returns no body response except 401 status code. [ProducesResponseType(StatusCodes.Status401Unauthorized)) is showing returning the following in swagger example

{
  "type": "string",
  "title": "string",
  "status": 0,
  "detail": "string",
  "instance": "string",
  "additionalProp1": {},
  "additionalProp2": {},
  "additionalProp3": {}
}