title: Error: trying to diff 'value' Only arrays and iterables are allowed
body: <p>I have a component to add multiple values. When i tried to set its value using patch value, i get the error "error trying to diff  'oatMeal' Only arrays and iterables are allowed" how can i update its value?</p>
  
  <p>Here is the code in plunker:<a href="https://plnkr.co/edit/hfiJ3SQokGjOwsf9OviG?p=preview" rel="nofollow noreferrer">https://plnkr.co/edit/hfiJ3SQokGjOwsf9OviG?p=preview</a></p>
  
  <p>This is the method i call to update the form field</p>
  
  <pre><code>updateForm() {
        this.formGroup.patchValue({venueAmenities: 'oatmeal'});
  }
  </code></pre>