title: Property 'array' does not exist on type 'FormGroup
body: <pre><code>import { FormBuilder, FormGroup, Validators, FormArray } from '@angular/forms'
  
   ngOnInit() {
      this.subjectDesigneForm = this.formBuilder.group({
        items: this.subjectDesigneForm.array([this.createItem()])
      });
    }
  </code></pre>
  
  <blockquote>
    <p>items: this.subjectDesigneForm.<strong><em>array</em></strong>([this.createItem()])</p>
  </blockquote>
  
  <p>when i write this line error accrues Property 'array' does not exist on type 'FormGroup</p>