Frustrating NPE/NME from a bukkit plugin (Citizens 2 and Factions)

Question

So I'm writing a citizens 2 trait which is supposed to make NPC's faction-ownable, but I've hit some problems I can't resolve. Any help would be appreciated! This happens when I start the server up:

[19:32:26] [Server thread/WARN]: [Citizens] Task #67 for Citizens v2.0.22- 
SNAPSHOT (build 1487) generated an exception
java.lang.NullPointerException
at redcrafter.factioncontrol.FactionTrait.onAttach(FactionTrait.java:45) ~[?:?]
at net.citizensnpcs.api.trait.Trait.linkToNPC(Trait.java:46) ~[?:?]
at net.citizensnpcs.api.npc.AbstractNPC.addTrait(AbstractNPC.java:100) ~[?:?]
at net.citizensnpcs.api.npc.AbstractNPC.load(AbstractNPC.java:300) ~[?:?]
at net.citizensnpcs.npc.CitizensNPC.load(CitizensNPC.java:134) ~[?:?]
at net.citizensnpcs.api.npc.SimpleNPCDataStore.loadInto(SimpleNPCDataStore.java:59) ~[?:?]
at net.citizensnpcs.Citizens$2.run(Citizens.java:305) ~[?:?]
at org.bukkit.craftbukkit.v1_10_R1.scheduler.CraftTask.run(CraftTask.java:71) ~[minecraft_server.jar:git-Spigot-de459a2-51263e9]
at org.bukkit.craftbukkit.v1_10_R1.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:353) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at net.minecraft.server.v1_10_R1.MinecraftServer.D(MinecraftServer.java:723) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at net.minecraft.server.v1_10_R1.DedicatedServer.D(DedicatedServer.java:400) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at net.minecraft.server.v1_10_R1.MinecraftServer.C(MinecraftServer.java:668) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at net.minecraft.server.v1_10_R1.MinecraftServer.run(MinecraftServer.java:567) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_171]

And this happens when I rightclick an NPC

[19:35:28] [Server thread/ERROR]: Could not pass event NPCRightClickEvent to 
Citizens v2.0.22-SNAPSHOT (build 1487)
org.bukkit.event.EventException
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:306) ~[minecraft_server.jar:git-Spigot-de459a2-51263e9]
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[minecraft_server.jar:git-Spigot-de459a2-51263e9]
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:502) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:487) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at net.citizensnpcs.EventListen.onPlayerInteractEntity(EventListen.java:414) [Citizens(4).jar:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_171]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_171]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_171]
at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_171]
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:302) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:502) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:487) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at net.minecraft.server.v1_10_R1.PlayerConnection.a(PlayerConnection.java:1540) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at net.minecraft.server.v1_10_R1.PacketPlayInUseEntity.a(SourceFile:68) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at net.minecraft.server.v1_10_R1.PacketPlayInUseEntity.a(SourceFile:12) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at net.minecraft.server.v1_10_R1.PlayerConnectionUtils$1.run(SourceFile:13) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_171]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_171]
at net.minecraft.server.v1_10_R1.SystemUtils.a(SourceFile:45) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at net.minecraft.server.v1_10_R1.MinecraftServer.D(MinecraftServer.java:732) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at net.minecraft.server.v1_10_R1.DedicatedServer.D(DedicatedServer.java:400) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at net.minecraft.server.v1_10_R1.MinecraftServer.C(MinecraftServer.java:668) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at net.minecraft.server.v1_10_R1.MinecraftServer.run(MinecraftServer.java:567) [minecraft_server.jar:git-Spigot-de459a2-51263e9]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_171]
Caused by: java.lang.NoSuchMethodError: com.massivecraft.factions.entity.FactionColl.get(Ljava/lang/Object;)Lcom/massivecraft/factions/entity/Faction;
at redcrafter.factioncontrol.FactionTrait.getFaction(FactionTrait.java:54) ~[?:?]
at redcrafter.factioncontrol.FactionTrait.onClick(FactionTrait.java:37) ~[?:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_171]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_171]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_171]
at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_171]
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:302) ~[minecraft_server.jar:git-Spigot-de459a2-51263e9]
... 24 more

And here is my code:

package redcrafter.factioncontrol;

import java.util.UUID;

import org.bukkit.Bukkit;
import org.bukkit.OfflinePlayer;
import org.bukkit.event.EventHandler;

import com.massivecraft.factions.Rel;
import com.massivecraft.factions.entity.Faction;
import com.massivecraft.factions.entity.FactionColl;
import com.massivecraft.factions.entity.MPlayer;

import net.citizensnpcs.api.event.NPCRightClickEvent;
import net.citizensnpcs.api.persistence.Persist;
import net.citizensnpcs.api.trait.Trait;
import net.citizensnpcs.api.trait.TraitName;
import net.citizensnpcs.api.trait.trait.Owner;

@TraitName("faction")
public class FactionTrait extends Trait {

    @Persist
    private String originalOwner;

    @Persist
    private String faction;

    public FactionTrait() {
        super("faction");
    }

    @EventHandler
    public void onClick(NPCRightClickEvent e) {
        if(e.getNPC() != getNPC()) return;
        Faction f = MPlayer.get(e.getClicker()).getFaction();
        if((f.getId().equals(getFaction().getId()) && (MPlayer.get(e.getClicker()).getRelationTo(f) == Rel.OFFICER || MPlayer.get(e.getClicker()).getRelationTo(f) == Rel.LEADER))
        || e.getClicker().getUniqueId().toString().equals(originalOwner)) {
            getNPC().getTrait(Owner.class).setOwner(e.getClicker());
            e.getClicker().sendMessage("Revokable ownership of the NPC transferred to you!");
        }
    }

    public void onAttach() {
        originalOwner = getNPC().getTrait(Owner.class).getOwnerId().toString();
        faction = FactionColl.get().getNone().getId();
    }

    public void setFaction(Faction f) {
        faction = f.getId();
    }

    public Faction getFaction() {
        if(FactionColl.get().containsId(faction)) return FactionColl.get().get(faction);
        setFaction(FactionColl.get().getNone());
        return FactionColl.get().getNone();
    }

    public OfflinePlayer getOriginalOwner() {
        return Bukkit.getOfflinePlayer(UUID.fromString(originalOwner));
    }

    public void setOriginalOwner(OfflinePlayer p) {
        originalOwner = p.getUniqueId().toString();
    }
}

It appears that the method FactionsColl.get() does not exist which does not make sense as the code compiles just fine. As for the NPE, I have no idea what could be causing it.

Possible duplicate of [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — LeoColman, May 29 '18 at 18:01

score 0 · Answer 1 · answered Jun 01 '18 at 06:37

The error you are getting is on line

originalOwner = getNPC().getTrait(Owner.class).getOwnerId().toString();

A Null Pointer Exception can occur when you call a method on something that returned null.

Due to the length of the line, it's very hard to debug from the trace where the error is.

You will either need to split this over multiple lines, or use the debugger to find where the null is.

It could be .getNPC returning null but we are unable to tell you, as you havn't provided code for getNPC.

It could also be .getTrait returning null.

Frustrating NPE/NME from a bukkit plugin (Citizens 2 and Factions)

1 Answers1