Description: Exception in server tick loop

java.lang.IllegalArgumentException: Invalid UUID string:
at java.util.UUID.fromString(UUID.java:194)
at com.darkona.adventurebackpack.handlers.GeneralEventHandler.makeHorsesFollowOwner(GeneralEventHandler.java:123)
at cpw.mods.fml.common.eventhandler.ASMEventHandler_11_GeneralEventHandler_makeHorsesFollowOwner_EntityJoinWorldEvent.invoke(.dynamic)
at cpw.mods.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:54)
at cpw.mods.fml.common.eventhandler.EventBus.post(EventBus.java:138)
at net.minecraft.world.World.func_72868_a(World.java:3300)
at net.minecraft.world.chunk.Chunk.func_76631_c(Chunk.java:921)
at net.minecraftforge.common.chunkio.ChunkIOProvider.callStage2(ChunkIOProvider.java:46)
at net.minecraftforge.common.chunkio.ChunkIOProvider.callStage2(ChunkIOProvider.java:12)
at net.minecraftforge.common.util.AsynchronousExecutor.skipQueue(AsynchronousExecutor.java:344)
at net.minecraftforge.common.util.AsynchronousExecutor.getSkipQueue(AsynchronousExecutor.java:302)
at net.minecraftforge.common.chunkio.ChunkIOExecutor.syncChunkLoad(ChunkIOExecutor.java:12)
at net.minecraft.world.gen.ChunkProviderServer.loadChunk(ChunkProviderServer.java:126)
at net.minecraft.world.gen.ChunkProviderServer.func_73158_c(ChunkProviderServer.java:101)
at net.minecraft.server.MinecraftServer.func_71222_d(MinecraftServer.java:265)
at net.minecraft.server.integrated.IntegratedServer.func_71247_a(IntegratedServer.java:78)
at net.minecraft.server.integrated.IntegratedServer.func_71197_b(IntegratedServer.java:92)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:387)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685)