I'm not sure the cause of the error or how to duplicate it.

[20:35:49 ERROR]: Could not pass event NPCRightClickEvent to Quests v2.7.3-b116
org.bukkit.event.EventException
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:310) ~[spigot.jar:git-Spigot-e0e1771-5e5cf84]
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[spigot.jar:git-Spigot-e0e1771-5e5cf84]
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:502) [spigot.jar:git-Spigot-e0e1771-5e5cf84]
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:487) [spigot.jar:git-Spigot-e0e1771-5e5cf84]
at net.citizensnpcs.EventListen.onPlayerInteractEntity(EventListen.java:404) [Citizens.jar:?]
at sun.reflect.GeneratedMethodAccessor275.invoke(Unknown Source) ~[?:?]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_101]
at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_101]
at me.incomprehendable.dev.pwp.transparentlisteners.PerWorldPluginLoader$1.execute(PerWorldPluginLoader.java:116) [PerWorldPlugins.jar:?]
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) [spigot.jar:git-Spigot-e0e1771-5e5cf84]
at me.incomprehendable.dev.pwp.transparentlisteners.PWPRegisteredListener.callEvent(PWPRegisteredListener.java:28) [PerWorldPlugins.jar:?]
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:502) [spigot.jar:git-Spigot-e0e1771-5e5cf84]
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:487) [spigot.jar:git-Spigot-e0e1771-5e5cf84]
at net.minecraft.server.v1_10_R1.PlayerConnection.a(PlayerConnection.java:1533) [spigot.jar:git-Spigot-e0e1771-5e5cf84]
at de.robingrether.idisguise.management.channel.InjectedPlayerConnection1101.a(InjectedPlayerConnection1101.java:59) [iDisguise.jar:?]
at net.minecraft.server.v1_10_R1.PacketPlayInUseEntity.a(SourceFile:68) [spigot.jar:git-Spigot-e0e1771-5e5cf84]
at net.minecraft.server.v1_10_R1.PacketPlayInUseEntity.a(SourceFile:12) [spigot.jar:git-Spigot-e0e1771-5e5cf84]
at net.minecraft.server.v1_10_R1.PlayerConnectionUtils$1.run(SourceFile:13) [spigot.jar:git-Spigot-e0e1771-5e5cf84]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_101] at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_101]
at net.minecraft.server.v1_10_R1.SystemUtils.a(SourceFile:45) [spigot.jar:git-Spigot-e0e1771-5e5cf84]
at net.minecraft.server.v1_10_R1.MinecraftServer.D(MinecraftServer.java:732) [spigot.jar:git-Spigot-e0e1771-5e5cf84]
at net.minecraft.server.v1_10_R1.DedicatedServer.D(DedicatedServer.java:400) [spigot.jar:git-Spigot-e0e1771-5e5cf84]
at net.minecraft.server.v1_10_R1.MinecraftServer.C(MinecraftServer.java:668) [spigot.jar:git-Spigot-e0e1771-5e5cf84]
at net.minecraft.server.v1_10_R1.MinecraftServer.run(MinecraftServer.java:567) [spigot.jar:git-Spigot-e0e1771-5e5cf84]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_101]
Caused by: java.lang.NullPointerException
at org.bukkit.inventory.ItemStack.(ItemStack.java:68) ~[spigot.jar:git-Spigot-e0e1771-5e5cf84]
at me.blackvein.quests.Quester.deliverItem(Quester.java:1404) ~[?:?]
at me.blackvein.quests.NpcListener.onNPCRightClick(NpcListener.java:74) ~[?:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_101]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_101]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_101]
at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_101]
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:306) ~[spigot.jar:git-Spigot-e0e1771-5e5cf84]
... 25 more

Duplicate of #405