AFNetworking/AFNetworking — pull request #1763 by PerishableDave (2014-01-20 22:27:20+00:00)
Title: Added exception handling when removing an observer on a task.

When a background task is completed, the task may no longer be observed by AFURLSessionManager. In that case, a call to removeObserver will cause an exception. So a try/catch needs to be added to only remove the observer when it has an observer.