Description: Exception ticking world

java.lang.NullPointerException: Exception ticking world
	at net.minecraft.server.v1_9_R1.BlockCauldron.changeLevel(BlockCauldron.java:185)
	at net.minecraft.server.v1_9_R1.BlockCauldron.a(BlockCauldron.java:178)
	at net.minecraft.server.v1_9_R1.BlockCauldron.h(BlockCauldron.java:205)
	at net.minecraft.server.v1_9_R1.WorldServer.j(WorldServer.java:475)
	at net.minecraft.server.v1_9_R1.WorldServer.doTick(WorldServer.java:249)
	at net.minecraft.server.v1_9_R1.MinecraftServer.D(MinecraftServer.java:771)
	at net.minecraft.server.v1_9_R1.DedicatedServer.D(DedicatedServer.java:400)
	at net.minecraft.server.v1_9_R1.MinecraftServer.C(MinecraftServer.java:655)
	at net.minecraft.server.v1_9_R1.MinecraftServer.run(MinecraftServer.java:554)
	at java.lang.Thread.run(Thread.java:745)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
	at net.minecraft.server.v1_9_R1.BlockCauldron.changeLevel(BlockCauldron.java:185)
	at net.minecraft.server.v1_9_R1.BlockCauldron.a(BlockCauldron.java:178)
	at net.minecraft.server.v1_9_R1.BlockCauldron.h(BlockCauldron.java:205)
	at net.minecraft.server.v1_9_R1.WorldServer.j(WorldServer.java:475)
	at net.minecraft.server.v1_9_R1.WorldServer.doTick(WorldServer.java:249)