Chain Adjuster - Lock Nut?

I recently removed my rear wheel so that I could clean it up and check the bearings and such. I'm getting ready to put it back on now and I'm noticing that there is no locknut on the chain adjuster bolt. Is this normal? Or did the PO lose them or something. I just bought the bike back in October and I'm just noticing it. Both of the adjuster bolts are missing these, so I'm wondering if they actually use them? Thought it weird that there wouldn't be some mechanism to prevent the bolt from moving.

Am I right about this? If so, I guess I'll have to go to the hardware store tomorrow and pick one up.

Perfect, thank you very much Patton. Guess I'm off to the store tomorrow.

Thanks again.