title: How to make "ng-multiselect-dropdown" a required field in Anguar7?
body: <p>How can I make <code>ng-multiselect-dropdown</code> a required field, which must accept at least one selected item ?</p>
  
  <pre><code>&lt;ng-multiselect-dropdown
      [placeholder]="'Select countries'"
      [data]="countries"
      [(ngModel)]="countriesSelectedItems"
      [settings]="countriesDropdownSettings"
      (onSelect)="onItemSelect($event)"
      (onSelectAll)="onSelectAll($event)"
      name="countries"
      class="form-control"&gt;
  &lt;/ng-multiselect-dropdown&gt;
  </code></pre>