Error executing task
java.util.concurrent.ExecutionException: java.lang.NullPointerException
	at java.util.concurrent.FutureTask.report(FutureTask.java:122) ~[?:1.8.0_121]
	at java.util.concurrent.FutureTask.get(FutureTask.java:192) ~[?:1.8.0_121]
	at net.minecraft.util.Util.runTask(Util.java:26) [Util.class:?]
	at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:742) [MinecraftServer.class:?]
	at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:687) [MinecraftServer.class:?]
	at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:156) [IntegratedServer.class:?]
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:536) [MinecraftServer.class:?]
	at java.lang.Thread.run(Thread.java:745) [?:1.8.0_121]
Caused by: java.lang.NullPointerException
	at net.minecraftforge.items.SlotItemHandler.getStack(SlotItemHandler.java:76) ~[SlotItemHandler.class:?]
	at net.minecraft.inventory.Container.getInventory(Container.java:63) ~[Container.class:?]
	at net.minecraft.inventory.Container.addListener(Container.java:52) ~[Container.class:?]
	at net.minecraftforge.fml.common.network.internal.FMLNetworkHandler.openGui(FMLNetworkHandler.java:100) ~[FMLNetworkHandler.class:?]
	at net.minecraft.entity.player.EntityPlayer.openGui(EntityPlayer.java:2729) ~[EntityPlayer.class:?]
	at me.creepinson.blocks.BlockMobChamber.onBlockActivated(BlockMobChamber.java:61) ~[BlockMobChamber.class:?]
	at net.minecraft.server.management.PlayerInteractionManager.processRightClickBlock(PlayerInteractionManager.java:477) ~[PlayerInteractionManager.class:?]
	at net.minecraft.network.NetHandlerPlayServer.processRightClickBlock(NetHandlerPlayServer.java:706) ~[NetHandlerPlayServer.class:?]
	at net.minecraft.network.play.client.CPacketPlayerTryUseItemOnBlock.processPacket(CPacketPlayerTryUseItemOnBlock.java:68) ~[CPacketPlayerTryUseItemOnBlock.class:?]
	at net.minecraft.network.play.client.CPacketPlayerTryUseItemOnBlock.processPacket(CPacketPlayerTryUseItemOnBlock.java:13) ~[CPacketPlayerTryUseItemOnBlock.class:?]
	at net.minecraft.network.PacketThreadUtil$1.run(PacketThreadUtil.java:15) ~[PacketThreadUtil$1.class:?]
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) ~[?:1.8.0_121]
	at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[?:1.8.0_121]
	at net.minecraft.util.Util.runTask(Util.java:25) ~[Util.class:?]
	... 5 more
[08:47:03] [Server thread/ERROR]: Encountered an unexpected exception
net.minecraft.util.ReportedException: Ticking player
	at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:789) ~[MinecraftServer.class:?]
	at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:687) ~[MinecraftServer.class:?]
	at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:156) ~[IntegratedServer.class:?]
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:536) [MinecraftServer.class:?]
	at java.lang.Thread.run(Thread.java:745) [?:1.8.0_121]
Caused by: java.lang.NullPointerException
	at net.minecraftforge.items.SlotItemHandler.getStack(SlotItemHandler.java:76) ~[SlotItemHandler.class:?]
	at net.minecraft.inventory.Container.detectAndSendChanges(Container.java:85) ~[Container.class:?]
	at net.minecraft.entity.player.EntityPlayerMP.onUpdate(EntityPlayerMP.java:292) ~[EntityPlayerMP.class:?]
	at net.minecraft.world.World.updateEntityWithOptionalForce(World.java:2111) ~[World.class:?]
	at net.minecraft.world.WorldServer.updateEntityWithOptionalForce(WorldServer.java:874) ~[WorldServer.class:?]
	at net.minecraft.world.World.updateEntity(World.java:2078) ~[World.class:?]
	at net.minecraft.world.WorldServer.tickPlayers(WorldServer.java:675) ~[WorldServer.class:?]
	at net.minecraft.world.World.updateEntities(World.java:1867) ~[World.class:?]
	at net.minecraft.world.WorldServer.updateEntities(WorldServer.java:646) ~[WorldServer.class:?]
	at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:783) ~[MinecraftServer.class:?]
	... 4 more