code: function koaConnect(connectMiddleware) {
    const handler = connectMiddleware.length < 3
      ? noCallbackHandler
      : withCallbackHandler
    return function koaConnect(ctx, next) {
      return handler(ctx, connectMiddleware, next)
    }
  }
docs: Returns a Koa middleware function that varies its async logic based on if the
  given middleware function declares at least 3 parameters, i.e. includes
  the `next` callback function