Error Message

[02:11:07] [Server thread/INFO] [STDOUT]: [com.limplungs.blockhole.DoubleLinkedQueue:writeNBT:57]: NODE DATA STARTING SAVE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
[02:11:07] [Server thread/INFO] [STDOUT]: [com.limplungs.blockhole.DoubleLinkedQueue:writeNBT:66]: Block{blockhole:teleporter}   .write.
[02:11:07] [Server thread/INFO] [STDOUT]: [com.limplungs.blockhole.DoubleLinkedQueue:writeNBT:66]: Block{blockhole:teleporter}   .write.
[02:11:07] [Server thread/INFO] [STDOUT]: [com.limplungs.blockhole.DoubleLinkedQueue:writeNBT:66]: Block{blockhole:teleporter}   .write.
[02:11:07] [Server thread/ERROR]: Encountered an unexpected exception
net.minecraft.util.ReportedException: Exception ticking world
	at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:778) ~[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(Unknown Source) [?:1.8.0_111]
Caused by: java.lang.NullPointerException
	at com.limplungs.blockhole.DoubleLinkedQueue.writeNBT(DoubleLinkedQueue.java:65) ~[DoubleLinkedQueue.class:?]
	at com.limplungs.blockhole.tileentities.TileEntityTeleporter.writeToNBT(TileEntityTeleporter.java:28) ~[TileEntityTeleporter.class:?]
	at com.limplungs.blockhole.tileentities.TileEntityTeleporter.getUpdateTag(TileEntityTeleporter.java:84) ~[TileEntityTeleporter.class:?]