first argument must be a string of Buffer

Hi, I was running some code and got this error message:

_http_outgoing.js:441
    throw new TypeError('first argument must be a string or Buffer');
    ^

TypeError: first argument must be a string or Buffer
    at ClientRequest.OutgoingMessage.write (_http_outgoing.js:441:11)
    at Request.write (/Users/tomasnovella/workspace/kitt/kitt-chrome-sync/node_modules/request/request.js:1392:25)
    at end (/Users/tomasnovella/workspace/kitt/kitt-chrome-sync/node_modules/request/request.js:550:16)
    at Immediate._onImmediate (/Users/tomasnovella/workspace/kitt/kitt-chrome-sync/node_modules/request/request.js:578:7)
    at processImmediate [as _immediateCallback] (timers.js:383:17)

Funny thing is, that if I replace the current version of request module with an older one(### v2.60.0 (2015/07/21), according to changelog), everything works just fine.

The code that causes this error is this:

  request.post({
        url: '<someURL>',
        qs: {
          'client': 'Google+Chrome',
          'client_id': config.clientId
        },
        headers: {
          'Content-Type': 'application/octet-stream',
          'Authorization': 'Bearer '+ accessToken
        },
        encoding: null, //  if you expect binary data
        responseType: 'buffer', 
        body: body
    }, (error, response, body) => {..blah...});