Bug fix: applet won't start due to a callback error.

The applet would not show on my taskbar until I removed the null callback value from bindProperty. I'm running Mint 15 with Cinnamon 1.8

My solution isn't elegant, since we now have a useless function cluttering the code. If you want me to replace this with a different function call, let me know. As long as the value is a valid function and not null, the problem is fixed.