It is normal for young hens who just started laying to lay eggs without a yolk occasionally. Some older hens will also if they were just molting and are starting laying again. I think they are called "fart eggs" LOL
It's normal-ish. When something comes down the reproductive pipe, it gets wrapped up in a white and shell. Usually that 'something' is a yolk, but sloughed tissue* can trigger the eggmaking process. Do you know who laid the egg? It might be a one-time thing caused by start or stop of lay, or it might be the first sign of reproductive issues. Probably it's the former and you won't be seeing another one any time soon. *or possibly nothing observable.
