My World Keeps Crashing Because I am Right Clicking my Spawning Catalyst.

So I was trying to make a block that when right clicked with the right item, would summon a boss. I place it in my Minecraft world and right click with the item used to activate the mechanism; then my game crashes. 

Here is the code I have for it: .

Here is the error message I get: https://pastebin.com/nBdVtXEL

If anyone is able to help, it would be much appreciated!