Check if SD card is inserted in device?

This Adobe documentation indicates you can use File.userDirectory to save files to the SD card on Android. The documentation doesn't point out that File.userDirectory will simply map to local storage if no SD card is inserted, making it useless for determining if an SD card is present. We are trying to give users of our app the option to save downloaded content to local storage or the SD card but we'd like to be able to verify an SD card exists first; is there any way for AIR to check this?