title: Magical Record - fetch in main thread block ui, in background return nil
body: <p>I'm new to Magical Record, but already have seen a few questions on stackoverflow, and can't find an answer to my question.</p>
  
  <p>I have to find items with the predicate using this type of construction:</p>
  
  <pre><code>NSArray *result = [MOSomeItems MR_findAllWithPredicate:predicate];
  </code></pre>
  
  <p>On the main thread result returns some value, but the UI is freezing.</p>
  
  <p>When using this construction, result returns nil value:</p>
  
  <pre><code>dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
  NSArray *result = [MOSomeItems MR_findAllWithPredicate:predicate];
  });
  </code></pre>
  
  <p>What is the best practice for fetching data in background? </p>