Cannot read property 'code' of undefined

I try to test my web api via Postman sandbox. I send simple post request and must get 400 or 200 status code in response. pre-request script :

var req_header = {
    "Content-Type":"application/x-www-form-urlencoded"
};   
var req_body = {
      mode: 'urlencoded',
      urlencoded: [
            {key: "client_id", value : "----", disabled: false},
            {key: "grant_type", value: "---", disabled: false},
            {key: "username", value: "---", disabled: false}, 
            {key: "password", value : "---", disabled: false},
            ] };

function StartBrutt (){
for (i=0;i < 100; i++){
      pm.sendRequest({url:"https://...", method:'Post', header:req_header, body : req_body}, 
  function (err, res) {
  if (err) { console.log(err); } 
  pm.test(
      'Get Response Code ',
  function () {
    pm.expect(pm.response.code).to.be.oneOf([200, 400]) //not worked
    //pm.expect(pm.res!=null)  worked good
        });
    });
}
}
StartBrutt();

But I always to get an error :

TypeError: Cannot read property 'code' of undefined

I use 6.1.3 version of desktop app.

Where is my Error ?