title: How to find node exists in JSON
body: <p>I have following JSON</p>
  
  <pre><code>{"subscription": 
   {
   "callbackReference": "xyz" ,
   "criteria": "Vote",
   "destinationAddress": "3456" ,
    "notificationFormat" : "JSON"
   }
  }
  </code></pre>
  
  <p>I want to check whether "notificationFormat" elements exits there using JSONPath expression. I can get the value of above element using following JSONPath expression.</p>
  
  <pre><code>$.subscription.notificationFormat
  </code></pre>
  
  <p>Can I use similar kind of expression which returns boolean value checking whether elements exists ?</p>