Exception was throwing when postion facebook access token to server

this is the EXCEPTION below:
[Error] EXCEPTION: Uncaught (in promise): TypeError: null is not an object (evaluating ‘this.saveToken’)
** file:///Users/achouri/Library/Developer/CoreSimulator/Devices/75573A43-31C1-4128-8646-6450C3B0A597/data/Containers/Bundle/Application/0C5E5E74-AEEC-43C8-BF82-D4567782225B/cofeeApp.app/www/build/main.js:59202:17**
** invoke@file:///Users/achouri/Library/Developer/CoreSimulator/Devices/75573A43-31C1-4128-8646-6450C3B0A597/data/Containers/Bundle/Application/0C5E5E74-AEEC-43C8-BF82-D4567782225B/cofeeApp.app/www/build/polyfills.js:3:9099**
** onInvoke@file:///Users/achouri/Library/Developer/CoreSimulator/Devices/75573A43-31C1-4128-8646-6450C3B0A597/data/Containers/Bundle/Application/0C5E5E74-AEEC-43C8-BF82-D4567782225B/cofeeApp.app/www/build/main.js:36863:43**
** invoke@file:///Users/achouri/Library/Developer/CoreSimulator/Devices/75573A43-31C1-4128-8646-6450C3B0A597/data/Containers/Bundle/Application/0C5E5E74-AEEC-43C8-BF82-D4567782225B/cofeeApp.app/www/build/polyfills.js:3:9053**
** run@file:///Users/achouri/Library/Developer/CoreSimulator/Devices/75573A43-31C1-4128-8646-6450C3B0A597/data/Containers/Bundle/Application/0C5E5E74-AEEC-43C8-BF82-D4567782225B/cofeeApp.app/www/build/polyfills.js:3:6487**
** file:///Users/achouri/Library/Developer/CoreSimulator/Devices/75573A43-31C1-4128-8646-6450C3B0A597/data/Containers/Bundle/Application/0C5E5E74-AEEC-43C8-BF82-D4567782225B/cofeeApp.app/www/build/polyfills.js:3:4586**
** invokeTask@file:///Users/achouri/Library/Developer/CoreSimulator/Devices/75573A43-31C1-4128-8646-6450C3B0A597/data/Containers/Bundle/Application/0C5E5E74-AEEC-43C8-BF82-D4567782225B/cofeeApp.app/www/build/polyfills.js:3:9728**
** onInvokeTask@file:///Users/achouri/Library/Developer/CoreSimulator/Devices/75573A43-31C1-4128-8646-6450C3B0A597/data/Containers/Bundle/Application/0C5E5E74-AEEC-43C8-BF82-D4567782225B/cofeeApp.app/www/build/main.js:36854:47**
** invokeTask@file:///Users/achouri/Library/Developer/CoreSimulator/Devices/75573A43-31C1-4128-8646-6450C3B0A597/data/Containers/Bundle/Application/0C5E5E74-AEEC-43C8-BF82-D4567782225B/cofeeApp.app/www/build/polyfills.js:3:9671**
** runTask@file:///Users/achouri/Library/Developer/CoreSimulator/Devices/75573A43-31C1-4128-8646-6450C3B0A597/data/Containers/Bundle/Application/0C5E5E74-AEEC-43C8-BF82-D4567782225B/cofeeApp.app/www/build/polyfills.js:3:7093**
** i@file:///Users/achouri/Library/Developer/CoreSimulator/Devices/75573A43-31C1-4128-8646-6450C3B0A597/data/Containers/Bundle/Application/0C5E5E74-AEEC-43C8-BF82-D4567782225B/cofeeApp.app/www/build/polyfills.js:3:3678**
** invoke@file:///Users/achouri/Library/Developer/CoreSimulator/Devices/75573A43-31C1-4128-8646-6450C3B0A597/data/Containers/Bundle/Application/0C5E5E74-AEEC-43C8-BF82-D4567782225B/cofeeApp.app/www/build/polyfills.js:3:10877**
** file:///Users/achouri/Library/Developer/CoreSimulator/Devices/75573A43-31C1-4128-8646-6450C3B0A597/data/Containers/Bundle/Application/0C5E5E74-AEEC-43C8-BF82-D4567782225B/cofeeApp.app/www/build/polyfills.js:2:30128**
** handleError (main.js:54644)**
** handleError (main.js:113155)**
** next (main.js:34553:94)**
** (fonction anonyme) (main.js:36063)**
** __tryOrUnsub (main.js:46393)**
** next (main.js:46342)**
** _next (main.js:46295)**
** next (main.js:46259)**
** next (main.js:16421)**
** emit (main.js:36055)**
** triggerError (main.js:36905)**
** onHandleError (main.js:36884)**
** handleError (polyfills.js:3:9206)**
** runGuarded (polyfills.js:3:6733)**
** r (polyfills.js:3:3782)**
** i (polyfills.js:3:3831)**
** invoke (polyfills.js:3:10878)**
** (fonction anonyme) (polyfills.js:2:30129)**

there my code:
saveToken(fbToken){
let myHeader= new Headers({
“content-type”:“application/x-www-form-urlencoded”
});
let options= new RequestOptions({
headers: myHeader,
});
return this.http.post(‘https://httpbin.org/post’,JSON.stringify({'fbtoken’ : fbToken}),options)
.map(res=> res.json())}
doFbLogin(){
let permissions = new Array();
let nav = this.navCtrl;
//the permissions your facebook app needs from the user
permissions = [“public_profile”];

Facebook.login(permissions)
.then(function(response){
  let data= {};
  let userId = response.authResponse.userID;
  let accessToken = response.authResponse.accessToken;
  let link_api= "http://leader-of-solutions.ovh/wp-test.php";
  let params = new Array<string>();

alert(accessToken);
this.saveToken(accessToken).subscribe((res)=>{

console.log(res);
});

//Getting name and gender properties
  Facebook.api("/me?fields=name,gender", params).then(function(user) {
    user.picture = "https://graph.facebook.com/" + userId + "/picture?type=large";

    //now we have the users info, let's save it in the NativeStorage
    NativeStorage.setItem('user',
    {
      name: user.name,
      gender: user.gender,
      picture: user.picture
    })
    .then(function(){
     //nav.setRoot(Profile);


    }, function (error) {
      console.log(error);
    })
  })
}, function(error){
  console.log(error);
});

}