title: Cannot read property of undefined inside the row expansion
body: <p>Befote I wrote this question I checked most of similar cases to mine, but with no success. I'm trying to display <code>number</code> and <code>auth</code> inside expandable row - I'm using PrimeNG. No matter what I try, nothing works. Since I'm out of fuel for this problem I need your help.</p>
  
  <p>Simplified code:</p>
  
  <p><strong>JSON</strong></p>
  
  <pre><code>{
  "status": 0,
  "dallases": [{
      "vehicle_id": 17954,
      "dallassettings": "3",
      "dallasupdated": "False",
      "dallas_list": [{
          "number": 666111222,
          "auth": 3
      }, {
          "number": 666777888,
          "auth": 4
      }, {
          "number": 123454321,
          "auth": 4
      }]
  }
  }
  </code></pre>
  
  <p><strong>Service</strong></p>
  
  <pre><code>export class VehicleService {
      private defUrl = 'dummy.url';
  
  constructor(private http: Http) { }
  getVehicle(username?: string, password?: string) {
      const url = (!username || !password) ? this.defUrl : 'dummy.url' + username + '/' + Md5.hashStr(password);
      return this.http.get(url)
          .map(res =&gt; res.json());
  </code></pre>
  
  <p><strong>Component</strong></p>
  
  <pre><code>export class VehicleComponent implements OnInit {
  
    cols: any[];
  
    ngOnInit() {
      this.cols = [
        { field: 'vehicle_id', header: "Vehicle ID" },
        { field: 'dallassettings', header: 'Dallas settings' },
        { field: 'dallasupdated', header: 'Dallas updated' },
        { field: 'dallas_list', header: 'Dallas list' }
      ];
  
    public vehicles: GeneralVehicle[];
  
    constructor(private vehicleService: VehicleService, private router: Router) {
      this.vehicleService.getVehicle().subscribe(vehicle =&gt; {
        this.vehicles = vehicle;
      });
    }
  
  interface GeneralVehicle {
    status: number;
    dallases: Vehicle[];
  }
  
  interface Vehicle {
    vehicle_id: number;
    dallassettings: string;
    dallasupdated: string;
    dallas_list: DallasList[];
  }
  
  interface DallasList {
    number: number;
    auth: number;
  }
  </code></pre>
  
  <p><strong>Template</strong></p>
  
  <pre><code>&lt;div *ngIf="vehicles"&gt;
      &lt;p-dataTable [value]="vehicles.dallases" expandableRows="true"&gt;
          &lt;p-header&gt;List of vehicles: &lt;b&gt;{{currentUser}}&lt;/b&gt;&lt;/p-header&gt;
          &lt;p-column expander="true" styleClass="col-icon"&gt;&lt;/p-column&gt;
          &lt;p-column field="vehicle_id" header="Vehicle ID" [sortable]="true"&gt;&lt;/p-column&gt;
          &lt;p-column field="dallassettings" header="Dallas settings" [sortable]="true"&gt;&lt;/p-column&gt;
          &lt;p-column field="dallasupdated" header="Dallas updated" [sortable]="true"&gt;&lt;/p-column&gt;
          &lt;ng-template let-vehicle="value.dallas_list" pTemplate="rowexpansion"&gt; &lt;!-- the problem is here --&gt;
              &lt;div class="ui-grid ui-grid-responsive ui-fluid" style="font-size:16px;padding:20px"&gt;
                  &lt;div class="ui-grid-row"&gt;
                      &lt;div class="ui-grid-col-9"&gt;
                          &lt;div class="ui-grid ui-grid-responsive ui-grid-pad"&gt;
                              &lt;div class="ui-grid-row"&gt;
                                  &lt;div class="ui-grid-col-2 label"&gt;Number: &lt;/div&gt;
                                  &lt;div class="ui-grid-col-10"&gt;{{dallas_list.number}}&lt;/div&gt;
                              &lt;/div&gt;
                              &lt;div class="ui-grid-row"&gt;
                                  &lt;div class="ui-grid-col-2 label"&gt;Auth: &lt;/div&gt;
                                  &lt;div class="ui-grid-col-10"&gt;{{dallas_list.auth}}&lt;/div&gt;
                              &lt;/div&gt;
                          &lt;/div&gt;
                      &lt;/div&gt;
                  &lt;/div&gt;
              &lt;/div&gt;
          &lt;/ng-template&gt;
      &lt;/p-dataTable&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I'm expecting to be able to display all <code>number</code>s and <code>auth</code>s for each of the rows inside the expendable row.</p>