title: Restkit Serializing a Boolean from NSNumber
body: <p>One of managed objects has one attribute 'isMember' represented by NSNumber type. When serialize to Json post body by RestKit, it always give 0/1 instead of YES/NO or true/false. When mapping from json result to objects, RestKit is able to successfully turn YES/NO to NSNumber. What is the way to force serialize the boolean attribute to YES/NO or true/false?</p>
  
  <pre><code>Serialize: 0 -&gt; 0, 1 -&gt; 1
  
  Deserialize : YES/true -&gt; 1, NO/false -&gt; 0
  </code></pre>