title: In ESB How to check if a key exists in json response
body: <p>I'm new to ESB proxy services, 
  I'm getting JSON response from a Google service, I need to check if a specific key exists in the response, i.e. In the following json,<br>
  <code>{
    "kind":"$$$$",
    "totalItems":0
    }</code>  </p>
  
  <p>I need to check if totalItems exists in the response and I want to filter this in proxy-service itself.
  Thanks in advance</p>