Unhooking an Entity in PlayerFishEvent causes NPE

[cesoun]

Stack trace

[22:08:33 ERROR]: Failed to handle packet net.minecraft.network.protocol.game.ServerboundUseItemPacket@32d4e0dd, suppressing error
java.lang.NullPointerException: Cannot invoke "net.minecraft.world.entity.Entity.getDeltaMovement()" because "entity" is null
        at net.minecraft.world.entity.projectile.FishingHook.pullEntity(FishingHook.java:599) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.world.entity.projectile.FishingHook.retrieve(FishingHook.java:502) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.world.item.FishingRodItem.use(FishingRodItem.java:33) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.world.item.ItemStack.use(ItemStack.java:596) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.server.level.ServerPlayerGameMode.useItem(ServerPlayerGameMode.java:483) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.server.network.ServerGamePacketListenerImpl.handleUseItem(ServerGamePacketListenerImpl.java:2016) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.network.protocol.game.ServerboundUseItemPacket.handle(ServerboundUseItemPacket.java:39) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.network.protocol.game.ServerboundUseItemPacket.handle(ServerboundUseItemPacket.java:10) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.network.protocol.PacketUtils.lambda$ensureRunningOnSameThread$0(PacketUtils.java:55) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.server.TickTask.run(TickTask.java:18) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.util.thread.BlockableEventLoop.doRunTask(BlockableEventLoop.java:151) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.util.thread.ReentrantBlockableEventLoop.doRunTask(ReentrantBlockableEventLoop.java:24) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.server.MinecraftServer.doRunTask(MinecraftServer.java:1517) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.server.MinecraftServer.doRunTask(MinecraftServer.java:198) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.util.thread.BlockableEventLoop.pollTask(BlockableEventLoop.java:125) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.server.MinecraftServer.pollTaskInternal(MinecraftServer.java:1494) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.server.MinecraftServer.pollTask(MinecraftServer.java:1417) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.util.thread.BlockableEventLoop.managedBlock(BlockableEventLoop.java:135) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.server.MinecraftServer.waitUntilNextTick(MinecraftServer.java:1383) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1244) ~[paper-1.20.6.jar:git-Paper-68]
        at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:326) ~[paper-1.20.6.jar:git-Paper-68]
        at java.base/java.lang.Thread.run(Thread.java:1583) ~[?:?]

Plugin and Datapack List

> plugins
[22:18:37 INFO]: Server Plugins (5):
[22:18:37 INFO]: Bukkit Plugins:
[22:18:37 INFO]:  - CommandAPI, Economy, Lectern, LuckPerms, Regions

> datapack list
[22:19:14 INFO]: There are 3 data pack(s) enabled: [vanilla (built-in)], [file/bukkit (world)], [paper (built-in)]
[22:19:14 INFO]: There are no more data packs available

Actions to reproduce (if known)

1. Register a PlayerFishEvent Listener
2. Call event.getHook().setHookedEntity(null)
3. Hook an entity with a rod in-game and reel them in.
4. NPE is raised and suppressed in console.

Paper version

> version
[22:19:45 INFO]: This server is running Paper version git-Paper-68 (MC: 1.20.6) (Implementing API version 1.20.6-R0.1-SNAPSHOT) (Git: 711f82e)
You are running the latest version
Previous version: git-Paper-62 (MC: 1.20.6)

Other

@EventHandler
fun onPlayerFish(event: PlayerFishEvent) {
	// ...
	
	event.hook.hookedEntity = null
	// event.getHook().setHookedEntity(null) // java eqiv.
	
	// ...
}

[Machine-Maker]

Yeah, I suppose we can address this. Is there functionally any difference from your end between doing this and cancelling the event?

[cesoun]

Yeah, I suppose we can address this. Is there functionally any difference from your end between doing this and cancelling the event?

Cancelling the event prevents the player from reeling the rod in, requiring them to swap to another item first before being able to re-cast the rod.

Unhooking the entity allows the rod to reel and be re-cast without switching items which is useful for preventing rod pulling entities and is more functionally expected behavior.