title: NativeScript/Angular - TypeError: Cannot read property 'Symbol' of undefined
body: <p>I've got a page component which has a <code>FormBuilder</code> form:</p>
  
  <pre><code>public adForm: FormGroup = this.fb.group({
    questions: this.fb.array([])
  });
  </code></pre>
  
  <p>I pass <code>questions</code> down to a <code>&lt;questions&gt;</code> component:</p>
  
  <pre><code>&lt;questions [questions]="adForm.get('questions')"&gt;&lt;/questions&gt;
  </code></pre>
  
  <p>Which has a <code>@Input() questions: FormArray;</code> and uses this template:</p>
  
  <pre><code>&lt;StackLayout orientation="vertical"&gt;
    &lt;!-- If I comment out listview then it doesn't throw the error --&gt;
    &lt;ListView [items]="questions"&gt;
      &lt;ng-template let-question="item"&gt;
        &lt;Label [text]="question.model"&gt;&lt;/Label&gt;
      &lt;/ng-template&gt;
    &lt;/ListView&gt;
    &lt;Button class="btn btn-md btn-primary" text="Add question" (tap)="addQuestion()"&gt;&lt;/Button&gt;
  &lt;/StackLayout&gt;
  </code></pre>
  
  <p>The problem I'm facing is that the <code>ListView</code> bit throws this error:</p>
  
  <pre><code>TypeError: Cannot read property 'Symbol' of undefined
  </code></pre>
  
  <p>If I comment that section out then it doesn't throw the error.</p>
  
  <p>I know it has something to do with the <code>questions</code> form array, but I haven't been able to figure out what. It is defined so it shouldn't be an issue having to do with something getting <code>undefined</code> instead of an empty array.. </p>
  
  <p>Note that this error is being thrown directly on component init. I've logged <code>questions</code> in the <code>ngOnInit</code> and it's not undefined.</p>
  
  <p>What am I doing wrong?</p>