Server: Paper-138 (1.16.1)
Way to reproduce: Fill a bucket with water.
Multiverse-Portals version: v4.1.1

https://gist.github.com/AndiSlash0723/2516497641875a376df008d3409b0014

[02:59:49 ERROR]: Could not pass event PlayerBucketFillEvent to Multiverse-Portals v4.1.1-SNAPSHOT-bUNKNOWN java.lang.NullPointerException: null at com.onarandombox.MultiversePortals.listeners.MVPPlayerListener.playerBucketFill(MVPPlayerListener.java:71) ~[?:?] at com.destroystokyo.paper.event.executor.asm.generated.GeneratedEventExecutor182.execute(Unknown Source) ~[?:?] at org.bukkit.plugin.EventExecutor.lambda$create$1(EventExecutor.java:69) ~[patched_1.16.1.jar:git-Paper-138] at co.aikar.timings.TimedEventExecutor.execute(TimedEventExecutor.java:80) ~[patched_1.16.1.jar:git-Paper-138] at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:70) ~[patched_1.16.1.jar:git-Paper-138] at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:607) ~[patched_1.16.1.jar:git-Paper-138] at org.bukkit.craftbukkit.v1_16_R1.event.CraftEventFactory.getPlayerBucketEvent(CraftEventFactory.java:449) ~[patched_1.16.1.jar:git-Paper-138] at org.bukkit.craftbukkit.v1_16_R1.event.CraftEventFactory.callPlayerBucketFillEvent(CraftEventFactory.java:425) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.ItemBucket.a(ItemBucket.java:44) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.ItemStack.a(ItemStack.java:379) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.PlayerInteractManager.a(PlayerInteractManager.java:412) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.PlayerConnection.a(PlayerConnection.java:1527) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.PacketPlayInBlockPlace.a(PacketPlayInBlockPlace.java:28) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.PacketPlayInBlockPlace.a(PacketPlayInBlockPlace.java:5) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.PlayerConnectionUtils.lambda$ensureMainThread$1(PlayerConnectionUtils.java:23) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.TickTask.run(SourceFile:18) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.IAsyncTaskHandler.executeTask(IAsyncTaskHandler.java:136) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.IAsyncTaskHandlerReentrant.executeTask(SourceFile:23) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.IAsyncTaskHandler.executeNext(IAsyncTaskHandler.java:109) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.MinecraftServer.aZ(MinecraftServer.java:1137) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.MinecraftServer.executeNext(MinecraftServer.java:1130) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.IAsyncTaskHandler.awaitTasks(IAsyncTaskHandler.java:119) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.MinecraftServer.a(MinecraftServer.java:1204) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.MinecraftServer.v(MinecraftServer.java:1001) ~[patched_1.16.1.jar:git-Paper-138] at net.minecraft.server.v1_16_R1.MinecraftServer.lambda$a$0(MinecraftServer.java:177) ~[patched_1.16.1.jar:git-Paper-138] at java.lang.Thread.run(Thread.java:835) [?:?]

This might be fixed with #551.

Sorry I dont understand, since I dont really know how to use GitHub :(
The version I'm using was downloaded in Discord (as long as I remember, not sure if there are any new releases after that)

v4.2 have been released on bukkit site. @AndiSlash0723 may I ask if the issue still persist on the latest version of papermc and MV plugins?

Yes, the issue still persist on v4.2 plugin version and on 244 paper version (latest version is 246)

[13:38:03 ERROR]: Could not pass event PlayerBucketFillEvent to Multiverse-Portals v4.2.0-b826
java.lang.NullPointerException: null
        at com.onarandombox.MultiversePortals.listeners.MVPPlayerListener.playerBucketFill(MVPPlayerListener.java:70) ~[?:?]
        at com.destroystokyo.paper.event.executor.asm.generated.GeneratedEventExecutor379.execute(Unknown Source) ~[?:?]
        at org.bukkit.plugin.EventExecutor.lambda$create$1(EventExecutor.java:69) ~[patched_1.16.3.jar:git-Paper-244]
        at co.aikar.timings.TimedEventExecutor.execute(TimedEventExecutor.java:80) ~[patched_1.16.3.jar:git-Paper-244]
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:70) ~[patched_1.16.3.jar:git-Paper-244]
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:607) ~[patched_1.16.3.jar:git-Paper-244]
        at org.bukkit.craftbukkit.v1_16_R2.event.CraftEventFactory.getPlayerBucketEvent(CraftEventFactory.java:454) ~[patched_1.16.3.jar:git-Paper-244]
        at org.bukkit.craftbukkit.v1_16_R2.event.CraftEventFactory.callPlayerBucketFillEvent(CraftEventFactory.java:430) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.ItemBucket.a(ItemBucket.java:44) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.ItemStack.a(ItemStack.java:379) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.PlayerInteractManager.a(PlayerInteractManager.java:414) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.PlayerConnection.a(PlayerConnection.java:1532) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.PacketPlayInBlockPlace.a(PacketPlayInBlockPlace.java:28) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.PacketPlayInBlockPlace.a(PacketPlayInBlockPlace.java:5) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.PlayerConnectionUtils.lambda$ensureMainThread$1(PlayerConnectionUtils.java:23) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.TickTask.run(SourceFile:18) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.IAsyncTaskHandler.executeTask(IAsyncTaskHandler.java:136) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.IAsyncTaskHandlerReentrant.executeTask(SourceFile:23) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.IAsyncTaskHandler.executeNext(IAsyncTaskHandler.java:109) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.MinecraftServer.ba(MinecraftServer.java:1135) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.MinecraftServer.executeNext(MinecraftServer.java:1128) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.IAsyncTaskHandler.executeAll(IAsyncTaskHandler.java:95) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.MinecraftServer.a(MinecraftServer.java:1264) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.MinecraftServer.w(MinecraftServer.java:999) ~[patched_1.16.3.jar:git-Paper-244]
        at net.minecraft.server.v1_16_R2.MinecraftServer.lambda$a$0(MinecraftServer.java:177) ~[patched_1.16.3.jar:git-Paper-244]
        at java.lang.Thread.run(Unknown Source) [?:1.8.0_261]

Thanks for letting us know. Can you please explain what you're doing when this happens? Or maybe take a video and show us.

I was not able to find an accurate and permanent way to reproduce the error, but it usually occurs when water/lava is collected in a bucket, last time player was collecting lava in second (not default) overworld in several buckets at once, but when I tried to do the same thing, nothing happened.
P.S. on paper 246 too.

Okay, that's fine. We will look into it when time permits.

I have the same issue. Happens when the player enters a nether portal.

I have the same problem.

Multiverse-Portals-4.2.0.jar
git-Paper-251

I can confirm this error is also happening with the latest Spigot and multiverse.

For people facing the issue, can you ensure you are on the latest version of mv plugins (v4.2.X) and send your full startup log as well as the output of /mvversion -p

It would be nice if you included a list of plugins, i.e. /mvversion -p --include-plugin-list.

One player reported that in between essentials:home teleports they crafted a bucket which refunded him 1/3 iron required. The refunded iron disappeared later and the error occurred when the bucket which had been filled with lava was emptied into water

This is happening on my server as well. When making an iron farm, the iron farm will work. After a while it stops working and when removing the water I get this same error.

@aaquino3 @AnmolMago can you please provide your full startup log as well as the link output of /mvversion -p.

@benwoo1110

Here is the server log. I removed some lines that contained chats and users logging in due to sensitive info like ip address. No errors happened during that time: https://pastebin.com/cZN7M4jQ

https://paste.gg/p/anonymous/1ece924dce6540369b4b3fd6cf6299ff

Paper Version: 261
Minecraft: 1.16.4

@benwoo1110 figured it out 🥳! This will be fixed by #590.

@nicegamer7 @benwoo1110 sweet, #590 looks like it needs some approval. When do we expect a build? I don't mind testing it

Not too sure when it'll be merged. But for now I've provided a build on the PRs thread.

Fixed in Release 4.2.1, thanks to everyone who participated!