Due to ARC, MGLOfflinePack can be deallocated at any time following its initialization. -dealloc ensures that the offline region observer is unset, but that step is asynchronous; there is no guarantee that it completes before the first status change update. In fact, the pack is deallocated before the first status change update unless it is captured outside of the MGLOfflinePackAdditionCompletionHandler. The pack nil check is unnecessary because the subsequent code would be a no-op.
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