title: What approach should I use when advertisingIdentifier is nil?
body: <p>According to apple docs, sometimes it happens that the method <code>[ASIdentifierManager sharedManager].advertisingIdentifier</code> can return a <code>nil</code> value and I really need this value in my app:</p>
  
  <p><a href="https://developer.apple.com/library/prerelease/ios/documentation/AdSupport/Reference/ASIdentifierManager_Ref/index.html#//apple_ref/occ/instp/ASIdentifierManager/advertisingIdentifier" rel="nofollow">https://developer.apple.com/library/prerelease/ios/documentation/AdSupport/Reference/ASIdentifierManager_Ref/index.html#//apple_ref/occ/instp/ASIdentifierManager/advertisingIdentifier</a></p>
  
  <blockquote>
    <p>If the value is nil, wait and get the value again later. This happens,
    for example, after the device has been restarted but before the user
    has unlocked the device.</p>
  </blockquote>
  
  <p>How long should I wait? What approach should I use in this case? Maybe keep trying to get the advertisingIdentifier until it is available? Or should I tell the user to try to restart the app? Any ideas?</p>
  
  <p>Thanks.</p>