Our server is crashing rather randomly while I'm running a custom plugin written by me which sets ALOT of blocks to water at a very fast speed. (I'm talking about 20k block changes per tick, at some times)

The world we currently have on this server is a custom world (http://www.planetminecraft.com/project/the-recreation-of-the-earth-11500-scale/), we only have it since a few days (I activated this plugin since we have this world). I'm not 100% sure if it might be caused by this world, but it seems kind of unlikely to me.

I suspect this has to do with the huge amount of block updates. The server lags quite badly, but it does manage to handle it. I have never experienced these crashes before I had this plugin doing huge amounts of block updates all the time.

I doubt one will be able to reproduce this easily, the crashes seem to happen rather randomly with quite often multiple hours of those block updates running inbetween.

The full crash report can be found at http://pastebin.com/xN3CKUej.

Whilst searching on the web I also found a somewhat similar issue: https://hub.spigotmc.org/jira/browse/SPIGOT-1337
That issue also has to do with a HashTreeSet#first() throwing a noSuchElementException after executing some obfuscated method in WorldServer when there are quite a few block updates, just like this one.