I've been getting this error whenever my players try to deliver an item to an NPC. It happens randomly... Sometimes it works fine, sometimes don't.
Is there a fix for this? Only solution so far is restart my server and my players quests...

13.07 04:36:47 [Server] Server thread/ERROR Could not pass event NPCRightClickEvent to Quests v3.7.4-b${env.BUILD_NUMBER}
13.07 04:36:47 [Server] INFO org.bukkit.event.EventException: null
13.07 04:36:47 [Server] INFO at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:320) ~[custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:70) ~[custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:529) ~[custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:514) ~[custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at net.citizensnpcs.EventListen.onPlayerInteractEntity(EventListen.java:469) ~[?:?]
13.07 04:36:47 [Server] INFO at sun.reflect.GeneratedMethodAccessor314.invoke(Unknown Source) ~[?:?]
13.07 04:36:47 [Server] INFO at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_212]
13.07 04:36:47 [Server] INFO at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_212]
13.07 04:36:47 [Server] INFO at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:316) ~[custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:70) ~[custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:529) ~[custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:514) ~[custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at net.minecraft.server.v1_14_R1.PlayerConnection.a(PlayerConnection.java:1846) ~[custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at net.minecraft.server.v1_14_R1.PacketPlayInUseEntity.a(SourceFile:69) ~[custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at net.minecraft.server.v1_14_R1.PacketPlayInUseEntity.a(SourceFile:13) ~[custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at net.minecraft.server.v1_14_R1.PlayerConnectionUtils.lambda$0(PlayerConnectionUtils.java:13) ~[custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at net.minecraft.server.v1_14_R1.TickTask.run(SourceFile:18) [custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at net.minecraft.server.v1_14_R1.IAsyncTaskHandler.executeTask(SourceFile:135) [custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at net.minecraft.server.v1_14_R1.IAsyncTaskHandlerReentrant.executeTask(SourceFile:23) [custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at net.minecraft.server.v1_14_R1.IAsyncTaskHandler.executeNext(SourceFile:114) [custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at net.minecraft.server.v1_14_R1.MinecraftServer.aW(MinecraftServer.java:898) [custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at net.minecraft.server.v1_14_R1.MinecraftServer.executeNext(MinecraftServer.java:891) [custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at net.minecraft.server.v1_14_R1.IAsyncTaskHandler.executeAll(SourceFile:99) [custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at net.minecraft.server.v1_14_R1.MinecraftServer.sleepForTick(MinecraftServer.java:874) [custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at net.minecraft.server.v1_14_R1.MinecraftServer.run(MinecraftServer.java:808) [custom.jar:git-Spigot-d05d3c1-7ad3a1f]
13.07 04:36:47 [Server] INFO at java.lang.Thread.run(Thread.java:748) [?:1.8.0_212]
13.07 04:36:47 [Server] INFO Caused by: java.lang.IndexOutOfBoundsException: Index: 1, Size: 1
13.07 04:36:47 [Server] INFO at java.util.LinkedList.checkElementIndex(LinkedList.java:555) ~[?:1.8.0_212]