title: Validate mat-autocomplete is object
body: <p>I'm new in Angular. I have a form in html:</p>
  
  <pre><code>   &lt;form class="input-form" [formGroup]='terminalsForm'&gt;
        &lt;mat-form-field class="form-full-width"&gt;
          &lt;input matInput placeholder="From" [matAutocomplete]="auto" formControlName='terminalInput' required&gt;
  
        &lt;/mat-form-field&gt;
  
        &lt;span&gt;Your choice is: {{terminalsForm.get('terminalInput').value | json}}&lt;/span&gt;
  
        &lt;mat-autocomplete #auto="matAutocomplete" [displayWith]="displayFn"&gt;
            &lt;mat-option *ngFor="let terminal of (filteredTerminals)?.results" [value]="terminal"&gt;
              &lt;span&gt;{{ terminal.name }}, {{terminal.city}}&lt;/span&gt;
            &lt;/mat-option&gt;
        &lt;/mat-autocomplete&gt;
      &lt;/form&gt;
  </code></pre>
  
  <p>It works fine and span indicate me if I selected an object or not (it returns a json with id included if I autocomplited object). How can I validate this field with select required? I need to pass terminal Id next so not selecting is supposed to be a validation error. Thanks!</p>