Ocean Monument structure does not have guardians spawning.

Put the summary of the bug you're having here

What I expected to happen was...:
Upon inspecting my guardian farm I created in 20w20b, I expected to see normal guardian spawn rates.

What actually happened was...:
Viewing my guardian farm in Pre-release 5 shows no guardian spawning attempts.

Steps to Reproduce:
1. Open up a new Minecraft World in Pre-release 5.
2. Located a Monument structure.
3.  You will see no guardian spawns at the monument.