[23:18:41] [Server thread/ERROR]: A TileEntity type com.example.DerpTesting.tile_entity.TileEntitySmallCrystal_Aqua has throw an exception trying to write state. It will not persist. Report this to the mod author
java.lang.RuntimeException: class com.example.DerpTesting.tile_entity.TileEntitySmallCrystal_Aqua is missing a mapping! This is a bug!
	at net.minecraft.tileentity.TileEntity.writeToNBT(TileEntity.java:80) ~[TileEntity.class:?]
	at net.minecraft.world.chunk.storage.AnvilChunkLoader.writeChunkToNBT(AnvilChunkLoader.java:370) [AnvilChunkLoader.class:?]
	at net.minecraft.world.chunk.storage.AnvilChunkLoader.saveChunk(AnvilChunkLoader.java:197) [AnvilChunkLoader.class:?]
	at net.minecraft.world.gen.ChunkProviderServer.safeSaveChunk(ChunkProviderServer.java:256) [ChunkProviderServer.class:?]
	at net.minecraft.world.gen.ChunkProviderServer.saveChunks(ChunkProviderServer.java:302) [ChunkProviderServer.class:?]
	at net.minecraft.world.WorldServer.saveAllChunks(WorldServer.java:808) [WorldServer.class:?]
	at net.minecraft.server.MinecraftServer.saveAllWorlds(MinecraftServer.java:318) [MinecraftServer.class:?]
	at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:106) [IntegratedServer.class:?]
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:427) [MinecraftServer.class:?]
	at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685) [MinecraftServer$2.class:?]