entity task error

[14:54:03.273] [Server thread/FATAL] [minecraft/MinecraftServer]: Error executing task
java.util.concurrent.ExecutionException: java.lang.NullPointerException
	at java.util.concurrent.FutureTask.report(Unknown Source) ~[?:1.8.0_131]
	at java.util.concurrent.FutureTask.get(Unknown Source) ~[?:1.8.0_131]
	at net.minecraft.util.Util.runTask(Util.java:127) [?:?]
	at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:770) [?:?]
	at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:724) [?:?]
	at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:122) [?:?]
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:611) [?:?]
	at java.lang.Thread.run(Unknown Source) [?:1.8.0_131]
Caused by: java.lang.NullPointerException
	at net.minecraft.entity.EntityTracker.track(EntityTracker.java:77) ~[?:?]
	at net.minecraft.world.ServerWorldEventHandler.onEntityAdded(ServerWorldEventHandler.java:39) ~[?:?]
	at net.minecraft.world.World.onEntityAdded(World.java:922) ~[?:?]
	at net.minecraft.world.WorldServer.onEntityAdded(WorldServer.java:836) ~[?:?]
	at net.minecraft.world.World.spawnEntity(World.java:915) ~[?:?]
	at net.minecraft.world.WorldServer.spawnEntity(WorldServer.java:796) ~[?:?]
	at tv.mapper.embellishcraft.block.BlockChair.onBlockActivated(BlockChair.java:53) ~[?:?]
	at net.minecraft.block.state.IBlockState.onBlockActivated(IBlockState.java:313) ~[?:?]
	at net.minecraft.server.management.PlayerInteractionManager.processRightClickBlock(PlayerInteractionManager.java:389) ~[?:?]
	at net.minecraft.network.NetHandlerPlayServer.processTryUseItemOnBlock(NetHandlerPlayServer.java:873) ~[?:?]
	at net.minecraft.network.play.client.CPacketPlayerTryUseItemOnBlock.processPacket(CPacketPlayerTryUseItemOnBlock.java:62) ~[?:?]
	at net.minecraft.network.play.client.CPacketPlayerTryUseItemOnBlock.processPacket(CPacketPlayerTryUseItemOnBlock.java:13) ~[?:?]
	at net.minecraft.network.PacketThreadUtil.lambda$checkThreadAndEnqueue$0(PacketThreadUtil.java:15) ~[?:?]
	at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) ~[?:1.8.0_131]
	at java.util.concurrent.FutureTask.run(Unknown Source) ~[?:1.8.0_131]
	at net.minecraft.util.Util.runTask(Util.java:126) ~[?:?]
	... 5 more