title: ReactiveForms hasError('required') always returning false
body: <p>In my Angular App, we have an array of inputs, for now we have the following going on:</p>
  
  <p><code>{{ item.valid }}</code> returns <code>false</code> in case the required validation was fulfilled -> <strong>That is correct</strong></p>
  
  <p>If we do: <code>item.hasError('required')</code> it returns false -> <strong>That is NOT correct</strong></p>
  
  <p>What do I need to make the <code>hasError</code> method to work?</p>
  
  <p>That is how we build our <strong>Reactive Form</strong>:</p>
  
  <pre><code>private buildForm(prices: Array&lt;Price&gt;, arrayName: string): FormArray {
      let controls = new FormArray([]);
  
      prognoseAngaben.forEach(price =&gt; {
        controls.push(new FormGroup(
          {
            value: new FormControl(price.value, [Validators.required, Validators.min(0)]),
          }));
      });
  
      this.myForm.setControl(arrayName, controls);
  
      return controls;
  }
  </code></pre>
  
  <p>And that is our HTML:</p>
  
  <pre><code>&lt;tbody [formArrayName]="arrayName"&gt;
      &lt;tr *ngFor="let item of myForm.controls[arrayName].controls; let i = index"&gt;
          &lt;ng-container [formGroupName]="i"&gt;
              &lt;kendo-numerictextbox [formControlName]="'value'" [format]="'n0'" [decimals]="0" [spinners]="false" [min]="0"&gt;&lt;/kendo-numerictextbox&gt;
          &lt;span&gt;{{item.hasError('required')}}&lt;/span&gt;
          &lt;span&gt;{{item.valid}}&lt;/span&gt;
          &lt;/ng-container&gt;
      &lt;/tr&gt;
  &lt;/tbody&gt;
  </code></pre>
  
  <p>What am I missing?</p>
  
  <p><strong>EDIT:</strong></p>
  
  <p>I create a Plunker with the answer:</p>
  
  <p><a href="https://plnkr.co/edit/l7gyONd4pLqqWGLGVjyb?p=preview" rel="nofollow noreferrer">https://plnkr.co/edit/l7gyONd4pLqqWGLGVjyb?p=preview</a></p>