No nether or end dimension

I got on minecraft to play test the new pre release snapshot to look for some bugs. And I noticed this huge game breaking bug that literally makes it so the end and the nether don't even exist. So I tried to make a nether portal to make sure it still works the same. It lets you create one, but when you walk through, the game crashes. Same for the end portal. Then, I tried using the /execute command to teleport into the dimension instead. When I typed "/execute in minecraft:" The only option was the overworld. So I have come to the conclusion that the end and nether don't exist. Please fix this soon. This is extremely game breaking.