title: Angular 6 Reactive Form field displays [object object] when first shown
body: <p>If my form field is defined as </p>
  
  <pre><code>occBarcodeProduct: new FormControl({ value: '', disabled: true, updateOn: 'blur'},
                                      Validators.required,
                                      null
  ),
  </code></pre>
  
  <p>the field shows the initial value :  <code>[object object]</code></p>
  
  <p>if the definition is reduced to :</p>
  
  <pre><code>occBarcodeProduct: new FormControl('',
                                      Validators.required,
                                      null
  ),
  </code></pre>
  
  <p>the field displays empty, as expected.</p>
  
  <p>I am new to Angular so not sure how to narrow the problem further.</p>