title: Realm Android - createOrUpdateAllFromJson, obtain objects not contained
body: <p>Using createOrUpdateAllFromJson from <a href="https://realm.io/docs/java/latest/#json" rel="nofollow noreferrer">Realm Android Documentation</a> I read:</p>
  
  <blockquote>
    <p>Parsing JSON with Realm is subject to the following rules.</p>
    
    <ol>
    <li>Creating object with JSON which has the field with a null value:
    
    <ul>
    <li>For a not-required field, set it to null which is the default value.</li>
    <li>For a required field, throw an exception.</li>
    </ul></li>
    <li>Updating object with JSON which has the field with a null value:
    
    <ul>
    <li>For a not-required field, set it to null.</li>
    <li>For a required field, throw an exception.</li>
    </ul></li>
    <li>JSON doesn’t have the field:
    
    <ul>
    <li>Leave the value unchanged for both required and not-required fields.</li>
    </ul></li>
    </ol>
  </blockquote>
  
  <p>Is there a way to obtain list of objects not contained in json (through the Primary Key)?</p>