pregenerator crash

[09:18:50] [Thread-26/INFO]: PreGenerator started generating land!
[09:18:50] [Thread-26/INFO]: Check console for details.
[09:18:50] [Thread-26/WARN]: Exception in thread "Thread-26"
[09:18:50] [Thread-26/WARN]: java.lang.IllegalStateException: Asynchronous entity world add!
[09:18:50] [Thread-26/WARN]: 	at org.spigotmc.AsyncCatcher.catchOp(AsyncCatcher.java:14)
[09:18:50] [Thread-26/WARN]: 	at net.minecraft.server.v1_8_R2.World.b(World.java:2642)
[09:18:50] [Thread-26/WARN]: 	at net.minecraft.server.v1_8_R2.Chunk.addEntities(Chunk.java:820)
[09:18:50] [Thread-26/WARN]: 	at net.minecraft.server.v1_8_R2.ChunkProviderServer.originalGetChunkAt(ChunkProviderServer.java:158)
[09:18:50] [Thread-26/WARN]: 	at net.minecraft.server.v1_8_R2.ChunkProviderServer.getChunkAt(ChunkProviderServer.java:118)
[09:18:50] [Thread-26/WARN]: 	at net.minecraft.server.v1_8_R2.ChunkProviderServer.getChunkAt(ChunkProviderServer.java:97)
[09:18:50] [Thread-26/WARN]: 	at org.bukkit.craftbukkit.v1_8_R2.CraftWorld.getChunkAt(CraftWorld.java:125)
[09:18:50] [Thread-26/WARN]: 	at Bammerbom.PreGenerator.Cuboid.generateChunks(Cuboid.java:619)
[09:18:50] [Thread-26/WARN]: 	at Bammerbom.PreGenerator.Main$1.run(Main.java:78)