title: Mapping empty array with RestKit
body: <p>Basically, I'm having the same problem as described <a href="https://stackoverflow.com/questions/9826310/object-mapping-an-empty-response-with-restkit">here</a>, but as I'm using a newer version of RestKit (v0.20.0-rc1 to be exact) I can't use the workaround mentioned in the answer.</p>
  
  <p>I'm trying to map an array of videos, which works fine as long as there is at least one object in the JSON response:</p>
  
  <pre><code>"videos": {"video": [
    {
     "id": 7066,
     "name": "firstVideo",
    },
    {
     "id": 7068,
     "name": "secondVideo",
    }
   ]}
  </code></pre>
  
  <p>When there are no videos I get this response:</p>
  
  <pre><code>"videos": ""
  </code></pre>
  
  <p>This causes my app to crash with the following message:</p>
  
  <pre><code>*** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[&lt;__NSCFConstantString 0x17db2d0&gt; valueForUndefinedKey:]: this class is not key value coding-compliant for the key video.'
  </code></pre>
  
  <p>Any help is appreciated.</p>