Missing cap or screw, rear wheel

[GANE]

My bike is quite new. I have spent the first tour, today.
Excepting a missing "something" (a screw or a cap), everything looks fine. The place of the missing part is shown in the attached picture. The question is if there is any oil bath or something like gears; normally not, is my opinion. Only the bearings? Inside is dry, I checked...
What is missing, there?

[GANE]

It can be useful just to send me a picture with a "normal" bike.

[Cornersruns]

Nothing missing there, it's a bolt.  It locks the chain adjuster.

[GANE]

Originally Posted by Cornersruns

Nothing missing there, it's a bolt.  It locks the chain adjuster.

So, is it OK with that uncovered hole!?

[Crow]

That is normal and is nothing to be worried about

[GANE]

Thanks!