I have the following error in my ionic project "Error: Uncaught (in promise): TypeError: Can not read property '0' of undefined"

Hello my Ionic project has the following error (Error: Uncaught (in promise): TypeError: Can not read property '0' of undefined) Attached is an image of the problem. I would like some hint Followtheprojectlink.

link

         login.ts

        import { Component } from '@angular/core';
       //import { NgForm } from '@angular/forms';

       import { NavController, ToastController } from 'ionic-angular';

        import { UserData } from '../../providers/user-data/user-data';
         import { AuthService } from 
       "../../providers/authservice/authservice";
        import { UserOptions } from '../../components/user-options/user-
         options';
       import { Storage } from "@ionic/storage";
        import { UserPage } from '../user/user';


        @Component({
           selector: 'page-user',
         templateUrl: 'login.html'
          })
       export class LoginPage {
         login: UserOptions = { username: '', password: '' };
       userData= {"username":"", "password":""};
         responseData: any;
       public userInfo: any;
        public dataSet: any;

       submitted = false;

        constructor(
        public navCtrl: NavController, 
       public loginData: UserData, 
       public authService: AuthService,
        public storage: Storage,
       public toastCtrl: ToastController
        ) { }

     //onLogin(form: NgForm) {
      onLogin() {
       this.submitted = true;
       this.dataSet = [];
      //var userdatalocal;

      if(this.userData.username && this.userData.password){
      //API connection
       this.authService.postData(this.userData, "login")
      .then((result) => {
       this.responseData = result;

      if(this.responseData){
      this.dataSet = this.responseData;


     //localStorage.setItem('userData',JSON.stringify(this.responseData));
     //this.storage.set('userData',JSON.stringify(this.responseData));
     this.userInfo = this.dataSet.userId[0].userData;
     // console.log(this.dataSet.userId[0].userData.email);

      this.loginData.login(this.userData.username); //para setar flag 
       loggedInMenu

      this.navCtrl.push(UserPage,this.dataSet);
    } else {
      // If login or password is invalid then return to LoginPage
      console.log("Erro18r: login/password invalid or bad connection");
      this.navCtrl.setPages([
        {page: LoginPage}
      ]) ;
      let toast = this.toastCtrl.create({
        message: this.responseData.error.text ,//'Login or password 
       incorrect.',
        duration: 5000
      });
      toast.present();
       }
       }, (err) => {
        //Connection failure message
       console.log(err);
        this.navCtrl.setPages([
         {page: LoginPage}
        ]) ;
          })
         } 
        }

          }