[08:31:04] [Server thread/ERROR]: Encountered an unexpected exception
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:926) ~[?:1.7.0_51]
at java.util.HashMap$EntryIterator.next(HashMap.java:966) ~[?:1.7.0_51]
at java.util.HashMap$EntryIterator.next(HashMap.java:964) ~[?:1.7.0_51]
at hats.common.core.HatHandler.getHatsWithWeightedContributors(HatHandler.java:582) ~[HatHandler.class:?]
at hats.common.core.EventHandler.onEntitySpawn(EventHandler.java:100) ~[EventHandler.class:?]
at cpw.mods.fml.common.eventhandler.ASMEventHandler_39_EventHandler_onEntitySpawn_EntityJoinWorldEvent.invoke(.dynamic) ~[?:?]
at cpw.mods.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:51) ~[ASMEventHandler.class:?]
at cpw.mods.fml.common.eventhandler.EventBus.post(EventBus.java:122) ~[EventBus.class:?]
at net.minecraft.world.World.addLoadedEntities(World.java:3570) ~[World.class:?]
at net.minecraft.world.chunk.Chunk.onChunkLoad(Chunk.java:1013) ~[Chunk.class:?]
at net.minecraftforge.common.chunkio.ChunkIOProvider.callStage2(ChunkIOProvider.java:46) ~[ChunkIOProvider.class:?]
at net.minecraftforge.common.chunkio.ChunkIOProvider.callStage2(ChunkIOProvider.java:12) ~[ChunkIOProvider.class:?]
at net.minecraftforge.common.util.AsynchronousExecutor.skipQueue(AsynchronousExecutor.java:344) ~[AsynchronousExecutor.class:?]
at net.minecraftforge.common.util.AsynchronousExecutor.getSkipQueue(AsynchronousExecutor.java:302) ~[AsynchronousExecutor.class:?]
at net.minecraftforge.common.chunkio.ChunkIOExecutor.syncChunkLoad(ChunkIOExecutor.java:12) ~[ChunkIOExecutor.class:?]
at net.minecraft.world.gen.ChunkProviderServer.loadChunk(ChunkProviderServer.java:140) ~[ChunkProviderServer.class:?]
at net.minecraft.world.gen.ChunkProviderServer.loadChunk(ChunkProviderServer.java:115) ~[ChunkProviderServer.class:?]
at net.minecraft.server.MinecraftServer.initialWorldChunkLoad(MinecraftServer.java:307) ~[MinecraftServer.class:?]
at net.minecraft.server.MinecraftServer.loadAllWorlds(MinecraftServer.java:277) ~[MinecraftServer.class:?]
at net.minecraft.server.dedicated.DedicatedServer.startServer(DedicatedServer.java:239) ~[DedicatedServer.class:?]
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:442) [MinecraftServer.class:?]
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:747) [MinecraftServer$2.class:?]