No response headers? No Cookies?

[blacksmoke26]

Failed to send response header(s)

/**
 * @public
 * @async
 * (Query) Get current user information
 * @returns {Promise<Object>}
 */
Query.test = async ( root, args, ctx, info ) => {
  /** @type {(fastify#FastifyReply|FastifyResponse)} */
  const res = ctx.res;
  res.header('X-test', 'changed');
  return true;
};

Response header:

< HTTP/1.1 200 OK
< X-XSS-Protection: 1; mode=block
< Vary: Origin
< Access-Control-Allow-Credentials: true
< x-test: changed
< content-type: application/json; charset=utf-8
< content-length: 2
< Date: Thu, 14 Feb 2019 17:18:54 GMT
< Connection: keep-alive

Header X-test wasn't sent to response, same issues with cookies.

[blacksmoke26]

This works great!

Query.test = async ( root, args, ctx, info ) => {
  /** @type {(fastify#FastifyReply|FastifyResponse)} */
  const res = ctx.res;
  res.header('X-test', 'changed')
    .send(true);
	
  //return true;
};

Response:

< Vary: Origin
< Access-Control-Allow-Credentials: true
< x-test: changed <--------------------------------------- here
< content-type: application/json; charset=utf-8
< content-length: 4
< Date: Thu, 14 Feb 2019 17:31:32 GMT
< Connection: keep-alive

So what you suggest, Can I use this to send headers/cookies in response?