NullPointerException when modifying any selection that contains natural spider spawners

The kind of small spider spawners that appear in tunnels in ocean biomes. Any set or replace operation over an area including one fails with the following:
[SERVER] java.lang.NullPointerException
[SERVER]        at net.canarymod.api.nbt.CanaryListTag.isEmpty(CanaryListTag.java:130)
[SERVER]        at net.canarymod.api.CanaryMobSpawnerLogic.getSpawns(CanaryMobSpawnerLogic.java:38)
[SERVER]        at com.minecraftonline.classicloader.classicapi.MobSpawnerLogic.getSpawn(MobSpawnerLogic.java:64)
[SERVER]        at CanaryWorld.copyFromWorld(CanaryWorld.java:512)
[SERVER]        at com.sk89q.worldedit.EditSession.rawGetBlock(EditSession.java:450)
[SERVER]        at com.sk89q.worldedit.EditSession.getBlock(EditSession.java:370)
[SERVER]        at com.sk89q.worldedit.EditSession.setBlock(EditSession.java:267)
[SERVER]        at com.sk89q.worldedit.EditSession.setBlocks(EditSession.java:1180)
[SERVER]        at com.sk89q.worldedit.commands.RegionCommands.set(RegionCommands.java:30)
[SERVER]        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[SERVER]        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
[SERVER]        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
[SERVER]        at java.lang.reflect.Method.invoke(Unknown Source)
[SERVER]        at com.sk89q.minecraft.util.commands.CommandsManager.invokeMethod(CommandsManager.java:428)
[SERVER]        at com.sk89q.worldedit.WorldEdit$1.invokeMethod(WorldEdit.java:211)
[SERVER]        at com.sk89q.worldedit.WorldEdit$1.invokeMethod(WorldEdit.java:154)
[SERVER]        at com.sk89q.minecraft.util.commands.CommandsManager.executeMethod(CommandsManager.java:421)
[SERVER]        at com.sk89q.minecraft.util.commands.CommandsManager.execute(CommandsManager.java:339)
[SERVER]        at com.sk89q.worldedit.WorldEdit.handleCommand(WorldEdit.java:1283)
[SERVER]        at CanaryWorldEditListener.onCommand(CanaryWorldEditListener.java:160)
[SERVER]        at com.minecraftonline.classicloader.classicapi.PluginLoader.callHook(PluginLoader.java:959)
[SERVER]        at com.minecraftonline.classicloader.classicapi.bridge.EventToHookAdapter.handleCommand(EventToHookAdapter.java:160)
[SERVER]        at sun.reflect.GeneratedMethodAccessor59.invoke(Unknown Source)
[SERVER]        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
[SERVER]        at java.lang.reflect.Method.invoke(Unknown Source)
[SERVER]        at net.canarymod.hook.HookExecutor$1.execute(HookExecutor.java:59)
[SERVER]        at net.canarymod.plugin.RegisteredPluginListener.execute(RegisteredPluginListener.java:52)
[SERVER]        at net.canarymod.hook.HookExecutor.callHook(HookExecutor.java:123)
[SERVER]        at net.canarymod.hook.Hook.call(Hook.java:37)
[SERVER]        at net.canarymod.api.entity.living.humanoid.CanaryPlayer.executeCommand(CanaryPlayer.java:247)
[SERVER]        at net.canarymod.api.entity.living.humanoid.CanaryPlayer.chat(CanaryPlayer.java:129)
[SERVER]        at net.minecraft.network.NetHandlerPlayServer.a(NetHandlerPlayServer.java:665)
[SERVER]        at net.minecraft.network.play.client.C01PacketChatMessage.a(C01PacketChatMessage.java:36)
[SERVER]        at net.minecraft.network.play.client.C01PacketChatMessage.a(C01PacketChatMessage.java:48)
[SERVER]        at net.minecraft.network.NetworkManager.a(NetworkManager.java:180)
[SERVER]        at net.minecraft.network.NetworkSystem.c(NetworkSystem.java:108)
[SERVER]        at net.minecraft.server.MinecraftServer.v(MinecraftServer.java:622)
[SERVER]        at net.minecraft.server.dedicated.DedicatedServer.v(DedicatedServer.java:367)
[SERVER]        at net.minecraft.server.MinecraftServer.u(MinecraftServer.java:526)
[SERVER]        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:430)
[SERVER]        at net.minecraft.server.MinecraftServer$3.run(MinecraftServer.java:742)
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