title: how to pass an object to amazon SNS
body: <p>I see in the examples how to to pass a message string to amazon sns sdk's publish method.  However, is there an exmaple of how to pass a custom object as the message?  I tried setting "MessageStructure" to "json" but then I get <code>InvalidParameter: Invalid parameter: Message Structure - No default entry in JSON message body</code> error.  Where should I be passing the object values into in the params?</p>
  
  <p>Any examples?</p>
  
  <pre><code>    var params = {
          Message: JSON.stringify(item),
          MessageStructure: 'json',
          TopicArn: topic
          //MessageAttributes: item
      };
  
      return sns.publishAsync(params);
  </code></pre>