title: PrimeNG dataTable: Using a p-checkbox inside a p-column causes Error
body: <p>I have this Datatable that works fine:</p>
  
  <pre><code>&lt;p-dataTable [value]="myObjects" [rows]="10" [paginator]="true" [pageLinks]="3"&gt;
      &lt;p-column field="name" header="Name"&gt;&lt;/p-column&gt;
      &lt;p-column field="size" header="Size"&gt;&lt;/p-column&gt;
      &lt;p-column field="status" header="Is available ?"&gt;
          &lt;ng-template let-col let-obj="rowData" pTemplate="body"&gt;
              &lt;input type="checkbox" [checked]="obj.status" [(ngModel)]="obj.status" /&gt;
          &lt;/ng-template&gt;
      &lt;/p-column&gt;
  &lt;/p-dataTable&gt;
  </code></pre>
  
  <p>Now I would like to <strong>replace</strong> the input type="checkbox" with a <strong>PrimeNG checkbox</strong>:</p>
  
  <pre><code>&lt;p-dataTable [value]="myObjects" [rows]="10" [paginator]="true" [pageLinks]="3"&gt;
      &lt;p-column field="name" header="Name"&gt;&lt;/p-column&gt;
      &lt;p-column field="size" header="Size"&gt;&lt;/p-column&gt;
      &lt;p-column field="status" header="Is available ?"&gt;
          &lt;ng-template let-col let-obj="rowData" pTemplate="body"&gt;
              &lt;p-checkbox [(ngModel)]="obj.status"&gt;&lt;/p-checkbox&gt;
          &lt;/ng-template&gt;
      &lt;/p-column&gt;
  &lt;/p-dataTable&gt;
  </code></pre>
  
  <p>This causes the following error (in the browser console). <strong>Why ? What am I missing ?</strong></p>
  
  <pre><code>core.es5.js:1020 ERROR Error: Uncaught (in promise): TypeError: this.model.indexOf is not a function
  TypeError: this.model.indexOf is not a function
      at Checkbox.isChecked (http://localhost:4200/vendor.bundle.js:110341:45)
      at Checkbox.writeValue (http://localhost:4200/vendor.bundle.js:110362:29)
  </code></pre>
  
  <p>Full stacktrace <a href="https://pastebin.com/VXFpbhx7" rel="noreferrer">here</a></p>