title: iOS (ObjC) PromiseKit - Return promise within promise
body: <p>I'm trying to cascade a promise through some classes which add functionality at each level. </p>
  
  <pre><code>+ (AnyPromise *) method {
      return [SomeClass whichReturnsPromise]
      .then(^(id obj){
          // do stuff
          return obj;
      });
    }
  </code></pre>
  
  <p>Unfortunately this code is throwing an error on the second line:</p>
  
  <p><strong><code>exc_bad_access (code=1 address=0x10)</code></strong></p>
  
  <p>(Note: just calling <code>return [SomeClass whichReturnsPromise]</code> works fine)</p>
  
  <p>I've scoured stackoverflow answers and tried many variations of the above code (which would work in javascript), but I keep getting the same error. How do I fix this?</p>