So i was messing around with a beacon using a tool to give it a custom effect, i was trying to get a good one for my arena, when i accidently typed effect id 21 wich caused the game to crash, and i was not able to enter the world again.

I know this actually is not a bug but it would be handy to add some kind of block to a beacon, that it first checks if the id is existing.

Steps to Reproduce:
1. Get a tool to change data on entity's (in this case nbtedit)
2. Select a beacon
3. Type under one of the 2 modes the id 21, and the game crashes