title: UIActivityViewController crashing on iOS 8 iPads
body: <p>I am currently testing my app with Xcode 6 (Beta 6). UIActivityViewController works fine with iPhone devices and simulators but crashes with iPad simulators and devices (iOS 8) with following logs</p>
  
  <pre><code>Terminating app due to uncaught exception 'NSGenericException', 
  reason: 'UIPopoverPresentationController 
  (&lt;_UIAlertControllerActionSheetRegularPresentationController: 0x7fc7a874bd90&gt;) 
  should have a non-nil sourceView or barButtonItem set before the presentation occurs.
  </code></pre>
  
  <p>I am using following code for iPhone and iPad for both iOS 7 as well as iOS 8</p>
  
  <pre><code>NSData *myData = [NSData dataWithContentsOfFile:_filename];
  NSArray *activityItems = [NSArray arrayWithObjects:myData, nil];
  UIActivityViewController *activityViewController = [[UIActivityViewController alloc] initWithActivityItems:nil applicationActivities:nil];
  activityViewController.excludedActivityTypes = @[UIActivityTypeCopyToPasteboard];
  [self presentViewController:activityViewController animated:YES completion:nil];
  </code></pre>
  
  <p>I am getting a similar crash in of one my other app as well. Can you please guide me ? has anything changed with UIActivityViewController in iOS 8? I checked but i did not find anything on this</p>