suggestion : a PARSE_ERROR event for the asset manager.

This helps clearly determining that the cause for getObject(someDataAsset) returning null is not from an IO_ERROR or the asset not existing in the first place.

 If this data was requested by the app to the user or an external source, we can implement a backup plan by listening for this event such as switching to a default set of data or reloading it from another source, or at least give the user or the external source the proper feedback.

(edit: sorry for the bad indentation I have no idea how that got through because it doesn't show up like this in my editor. i just wanted to go ahead with a pull request just to save you a bit of time)