title: Better way to determine if value exists in JSON feed
body: <p>I'm using the <code>org.json.JSONObject</code> (and parser) in an Android app to parse a JSON feed. Which is the best way to determine if a property exists or not in one of the objects returned?</p>
  
  <p>Say I have a JSON feed including "News". Some of the news have a property called "UnpublishDate" (which is the date the news in question is no longer active), while some of the news don't have this property.</p>
  
  <p>The best solution I've come up with (though not implemented yet) is to simply have a "try-catch" around the <code>theJSONObject.get("UnpublishDate")</code> - do you know of any better solution (that is more graceful when the class scales to several "optional" properties in the JSON feed)?</p>