Hi

http://pastebin.com/raw/bF6t6pEn

Is it reproducable? What were you looking at?

"hi" and a log is nowhere near enough information.

sorry
It was when I use "Tinsel Garland" in Fairy Lights mod
It happen 2 time and I removed HWYLA from the server.

After looking through the Fairy Lights Github, I can only assume the crash is on their end (if the crash is definitely being caused by the Garland). The line crashing is here. All that line is doing is getting the entities dimension. The entity has already been nullchecked at that point and there is no reason a null should be thrown later on.

Please report it to them.