What's inside a DS Lite slot cover?

The DS Lite, as most people probably know, comes with a placeholder gba cartridge that nintendo officially calls the "cartridge slot cover". This has electrical contacts on it, though it does nothing when inserted into the system.

I would assume there's nothing inside it besides a blank PCB with the contacts, but I can't seem to find any images confirming this, and I don't have a triwing screwdriver to open mine up.

Can anyone say definitively (with pictures if possible) what is inside one of these placeholder cartridges?

Solution 1:

The serial number for the cartridge is USG-005. The serial number on the PCB is C/USG-D01-01.