title: Give placeholder to select in Angular 6
body: <p>I have a select option in which i want to give placeholder which says "select a category"</p>
  
  <pre><code>&lt;form role="form" class="form form-horizontal" (ngSubmit)="onSubmit()" #form="ngForm" ngNativeValidate&gt;
          &lt;div class="form-group row"&gt;
              &lt;div class="col-xl-4 col-lg-6 col-md-12"&gt;
                  &lt;fieldset class="form-group"&gt;
                      &lt;label for="customSelect"&gt;Categories:&lt;/label&gt;
                      &lt;select class="custom-select d-block w-100" id="Category" [(ngModel)]="Category" name="Category" required&gt;
                          &lt;option value=" "&gt;Select one category &lt;/option&gt;                                     
                           &lt;option *ngFor="let item of myBusinessList" [value]="item.id"&gt;{{item.name}}&lt;/option&gt;
                      &lt;/select&gt;
                  &lt;/fieldset&gt;                                
              &lt;/div&gt;
          &lt;/div&gt;
          &lt;button type="submit" class="btn btn-raised btn-danger"&gt;Save&lt;/button&gt;
      &lt;/form&gt;
  </code></pre>
  
  <p>If i remove [ngModel] then it works. If i write </p>
  
  <pre><code>&lt;option value="undefined" selected&gt;Select one category &lt;/option&gt;    
  </code></pre>
  
  <p>then it considers as one of the value. I have to make sure there is place and also it is required to select one of the value</p>