Hey,
I'd like to have this plugin on my 1.15.2 Spigot server.
When I install the plugin, it says in the console:
[09:43:58] [Server thread/ERROR]: Error occurred while enabling StackableItems v1.0.10 (Is it up to date?) java.lang.NullPointerException: null at haveric.stackableItems.util.SIItems.loadItemsFile(SIItems.java:183) ~[?:?] at haveric.stackableItems.util.SIItems.reload(SIItems.java:113) ~[?:?] at haveric.stackableItems.util.SIItems.init(SIItems.java:76) ~[?:?] at haveric.stackableItems.StackableItems.onEnable(StackableItems.java:44) ~[?:?] at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:263) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:352) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:417) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.craftbukkit.v1_15_R1.CraftServer.enablePlugin(CraftServer.java:462) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.craftbukkit.v1_15_R1.CraftServer.enablePlugins(CraftServer.java:376) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.craftbukkit.v1_15_R1.CraftServer.reload(CraftServer.java:811) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.Bukkit.reload(Bukkit.java:576) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.command.defaults.ReloadCommand.execute(ReloadCommand.java:27) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:149) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.craftbukkit.v1_15_R1.CraftServer.dispatchCommand(CraftServer.java:711) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.craftbukkit.v1_15_R1.CraftServer.dispatchServerCommand(CraftServer.java:696) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.DedicatedServer.handleCommandQueue(DedicatedServer.java:436) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.DedicatedServer.b(DedicatedServer.java:400) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.MinecraftServer.a(MinecraftServer.java:984) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.MinecraftServer.run(MinecraftServer.java:824) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at java.lang.Thread.run(Unknown Source) [?:1.8.0_231]
And:
[09:44:36] [Server thread/ERROR]: Could not pass event InventoryClickEvent to StackableItems v1.0.10 org.bukkit.event.EventException: null at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:320) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:70) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:529) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:514) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.PlayerConnection.a(PlayerConnection.java:2147) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.PacketPlayInWindowClick.a(SourceFile:32) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.PacketPlayInWindowClick.a(SourceFile:10) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.PlayerConnectionUtils.lambda$0(PlayerConnectionUtils.java:19) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.TickTask.run(SourceFile:18) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.IAsyncTaskHandler.executeTask(SourceFile:144) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.IAsyncTaskHandlerReentrant.executeTask(SourceFile:23) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.IAsyncTaskHandler.executeNext(SourceFile:118) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.MinecraftServer.ba(MinecraftServer.java:918) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.MinecraftServer.executeNext(MinecraftServer.java:911) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.IAsyncTaskHandler.executeAll(SourceFile:103) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.MinecraftServer.sleepForTick(MinecraftServer.java:894) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.MinecraftServer.run(MinecraftServer.java:828) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at java.lang.Thread.run(Unknown Source) [?:1.8.0_231] Caused by: java.lang.IllegalArgumentException: Plugin cannot be null at org.apache.commons.lang.Validate.notNull(Validate.java:192) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.craftbukkit.v1_15_R1.scheduler.CraftScheduler.validate(CraftScheduler.java:443) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.craftbukkit.v1_15_R1.scheduler.CraftScheduler.runTaskTimer(CraftScheduler.java:176) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.craftbukkit.v1_15_R1.scheduler.CraftScheduler.runTaskTimer(CraftScheduler.java:167) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.craftbukkit.v1_15_R1.scheduler.CraftScheduler.runTaskLater(CraftScheduler.java:131) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at haveric.stackableItems.util.InventoryUtil.updateInventoryLater(InventoryUtil.java:958) ~[?:?] at haveric.stackableItems.listeners.SIPlayerListener.inventoryClick(SIPlayerListener.java:1486) ~[?:?] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_231] at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_231] at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_231] at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_231] at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:316) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] ... 17 more [09:44:36] [Server thread/ERROR]: Could not pass event InventoryClickEvent to StackableItems v1.0.10 org.bukkit.event.EventException: null at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:320) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:70) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:529) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:514) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.PlayerConnection.a(PlayerConnection.java:2147) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.PacketPlayInWindowClick.a(SourceFile:32) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.PacketPlayInWindowClick.a(SourceFile:10) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.PlayerConnectionUtils.lambda$0(PlayerConnectionUtils.java:19) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.TickTask.run(SourceFile:18) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.IAsyncTaskHandler.executeTask(SourceFile:144) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.IAsyncTaskHandlerReentrant.executeTask(SourceFile:23) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.IAsyncTaskHandler.executeNext(SourceFile:118) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.MinecraftServer.ba(MinecraftServer.java:918) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.MinecraftServer.executeNext(MinecraftServer.java:911) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.IAsyncTaskHandler.executeAll(SourceFile:103) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.MinecraftServer.sleepForTick(MinecraftServer.java:894) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at net.minecraft.server.v1_15_R1.MinecraftServer.run(MinecraftServer.java:828) [spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at java.lang.Thread.run(Unknown Source) [?:1.8.0_231] Caused by: java.lang.IllegalArgumentException: Plugin cannot be null at org.apache.commons.lang.Validate.notNull(Validate.java:192) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.craftbukkit.v1_15_R1.scheduler.CraftScheduler.validate(CraftScheduler.java:443) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.craftbukkit.v1_15_R1.scheduler.CraftScheduler.runTaskTimer(CraftScheduler.java:176) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.craftbukkit.v1_15_R1.scheduler.CraftScheduler.runTaskTimer(CraftScheduler.java:167) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at org.bukkit.craftbukkit.v1_15_R1.scheduler.CraftScheduler.runTaskLater(CraftScheduler.java:131) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] at haveric.stackableItems.util.InventoryUtil.updateInventoryLater(InventoryUtil.java:958) ~[?:?] at haveric.stackableItems.listeners.SIPlayerListener.inventoryClick(SIPlayerListener.java:1432) ~[?:?] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_231] at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_231] at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_231] at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_231] at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:316) ~[spigot-1.15.2.jar:git-Spigot-800b93f-8160e29] ... 17 more
Can you update the plugin, so it can be used in 1.15.2?

StackableItems should work just fine on 1.15.2 (and I've had no issues with it so far), which leads me to believe this is something else. One option might be that the jar got corrupted in the download which while rare, I have seen happen a few times. Can you try redownloading the latest version and trying a full restart to see if that fixes the issue?

Good to hear! If you want to have this work across all of your worlds for all players and inventories, you can set the following:

allWorlds:
  default:
    TOTEM_OF_UNDYING: 16

If you're looking for something more restrictive or have any issues with that, please stop by the discord and I'll be glad to help out more.

StackableItems should work just fine on 1.15.2 (and I've had no issues with it so far), which leads me to believe this is something else. One option might be that the jar got corrupted in the download which while rare, I have seen happen a few times. Can you try redownloading the latest version and trying a full restart to see if that fixes the issue?

I followed your instructions and it actually worked! Thank you!
1 More question not related to this issue subject thing: How do I increase the max stackable amount for totem of undying?
I want to be able to stack the totem of undying to 16. (That's why I installed this plugin) .
The instructions on the Bukkit website seems unclear to me. (No hate)
How do I do this?