A new setting in iTunes 12.2.1 may automatically hide your library from any 3rd party apps like Dapper.
To check this:
- Open iTunes
- From the iTunes menu, select "Preferences"
- Click on the "Advanced" tab gear
- Make sure "Share Library XML with other Applications" is checked.
- Quit iTunes
Dapper 2.2 (to be released in mid August) and above will detect this and prompt you to change your iTunes sharing settings, but earlier versions will not.
If you ave library thats been moved or is on an external drive, the library data may actually not be in the same place as your music files.
Have a look at this video to see what happens in this case: https://www.youtube.com/watch?v=-GPjP_WZUZU&t=1s