title: RestKit - Map JSON response with null value/empty array
body: <p>How do I gracefully handle an (expected) nil keypath during a RestKit GET?</p>
  
  <p>When I make a getAllEvents API call if the user doesn't have any events the API will return a null value in the payload, e.g. <code>{"events":null}</code>. The null value causes the RestKit <code>request: didFailLoadWithError</code> and <code>objectLoader: didFailWithError</code> methods to be invoked, which I don't necessarily want because this is the expected behavior where there are 0 events. The error message it gives is <code>Could not find an object mapping for keyPath: ''</code>.</p>
  
  <p>Can I handle this in the mapping config and/or the delegate methods, or do I need to modify the API, perhaps to return an empty string instead of null. Is there a standard for what JSON should return when the list is empty?</p>