title: Angular2: Property 'controls' does not exist on type 'AbstractControl'. Error when accessing .control of an object within a formarray thru an index
body: <p>I'm trying to push another formbuilder within a formarray but it gives me an error since I think there are no items in the array when initializing the code, hence there are no controls. The error is Property 'controls' does not exist on type 'AbstractControl' after the</p>
  
  <pre><code>(&lt;FormArray&gt;this.loanTypeForm.controls['frequency']).controls[index]
  </code></pre>
  
  <p>I'm using angular 2.0.0-beta.17</p>
  
  <pre><code>let settingsForm: FormArray = new FormArray([]);
        (&lt;FormArray&gt;this.loanTypeForm.controls['frequency']).push(
          this.formBuilder.group({
            'name': [value, Validators.required],
            'settings': settingsForm,
          })
        );
  (&lt;FormArray&gt;this.loanTypeForm.controls['frequency']).controls[index].controls['settings'].push(
        this.formBuilder.group({
          'term': [null, Validators.required],
          'eir': [null, Validators.required],
        })
      );
  </code></pre>