Please describe the problem:
If you have a song that has any empty field (in Artist name, Album name, or Title...), the MetaDataHash column will be broken because when generating it for the song in the DAP, it takes in account the helper "fake" unknown names ("Unknown Album", "Unknown Artist", "Unknown Title").


Steps to reproduce:
1. Import a song to the library that has some empty field.
2. Examine the database:
sqlite3 ~/.config/banshee-1/banshee.db
SQLite version 3.5.7
Enter ".help" for instructions
sqlite> SELECT Title,MetadataHash From CoreTracks;
Inspirited Vitality|bf85b668418f21eab4adcda96199c049
3. Connect your DAP and wait until it's synced (an iPod in my case).
4. Examine the database.


Actual results:
sqlite> SELECT Title,MetadataHash From CoreTracks;
Inspirited Vitality|bf85b668418f21eab4adcda96199c049
Inspirited Vitality|86736c11027e68436c1dddd55ac45939


Expected results:
They should have the same hash.

Does this happen every time?
Yes.

Other information:
This is causing some other bugs in the sync algorithms (for example in playlist syncing), because they rely heavily on the MetaDataHash field for comparing purposes.

This is one of the edge cases I was talking about in bug 560970.