Part number 1K0721989
It just makes it look finished. I got mine from LLLParts, it was only 39p, but unless you're buying other stuff the postage will add to that. You should be able to order it from a main dealer. It's not technically a Caddy part, I had to look up the part number on the Golf diagrams which share the same pedal.
I see some chancers on eBay have them for nearly £10 each, or £7 for a used one

