Promise.resolve doesn't work but return works

I have this function which returns a Promise

save(data) => {
    return mymongo.insert(data).then(
        (result) => { return Promise.resolve(result); }
    )
}

in my router I call that function

app.post('/printers', (req, res, next) => {
    save(req.body).then(
        (result) => {
            console.log('hello') // is not called, nothing is printed
            console.log(result) // is not called
            res.send(result)
        }
    ).catch(res.send);
});

then with curl I do the request

curl -v -d '{ ... }' -X POST http://localhost:8080/printers

It is pretty fast and looks fine, so no timeout but no response and in console there is no logs

*   Trying 127.0.0.1...
* TCP_NODELAY set
* Connected to localhost (127.0.0.1) port 8080 (#0)
> POST /printers HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.52.1
> Accept: */*
> Content-Length: 35
> Content-Type: application/x-www-form-urlencoded
> 
* upload completely sent off: 35 out of 35 bytes
< HTTP/1.1 200 OK
< X-Powered-By: Express
< Content-Type: application/json; charset=utf-8
< Content-Length: 2
< ETag: W/"2-vyGp6PvFo4RvsFtPoIWeCReyIC8"
< Date: Fri, 21 Apr 2017 01:01:30 GMT
< Connection: keep-alive
< 
* Curl_http_done: called premature == 0
* Connection #0 to host localhost left intact

when I replace return Promise.resolve(result) with return result then I receive the response from the server and console.log(result) gets executed and in my console I see

hello
{ .... }

via user7887107