With the new spawners being able to spawn all sorts of crazy things, I decided to try and make a Lightning Spawner in my private whitelisted server. I was using a plugin called CubeGenetics, which is an in-game NBT editor. Very useful and reliable. Never crashed before. When I changed the EntityId to Lightning and saved it to the spawner, all the sudden my minecraft window went the color of the sky and my game crashed. I do not think that it was caused by an incorrect string for EntityId, as I have entered nonexistent Ids in before without an issue.