title: Object to Json including only fields not null
body: <p>I have an object named Item with plenty of fields. I'm using a Java JSON (json-io) library to serialize its state in a File:</p>
  
  <pre><code>String json = JsonWriter.objectToJson(item);
  // Write String to File
  </code></pre>
  
  <p>I'd like to make the json String less verbose so that it does not include null values (if possible also boolean which are false). Is it possible to do it somehow ? <br/>
  Thanks</p>