Monsters not Spawning

I recently created a new survival world in the new 19w09a snapshot to see how the gameplay would play out when the WIP update is released. I spawned in the world and started doing the normal things, and I realized that there weren't any monsters spawning. At all. I went caving for about 30 minutes in a decent sized cave and there were no monsters. Not even at night.
I hope this gets fixed!