[22:42:16 ERROR]: Could not pass event PlayerQuitEvent to TradeMe v6.0.0.2

org.bukkit.event.EventException: null

at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:306) ~[minecraft_server.jar:git-Spigot-c3093ef-7e94e65]

at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[minecraft_server.jar:git-Spigot-c3093ef-7e94e65]

at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:500) [minecraft_server.jar:git-Spigot-c3093ef-7e94e65]

at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:485) [minecraft_server.jar:git-Spigot-c3093ef-7e94e65]

at net.minecraft.server.v1_12_R1.PlayerList.disconnect(PlayerList.java:405) [minecraft_server.jar:git-Spigot-c3093ef-7e94e65]

at net.minecraft.server.v1_12_R1.PlayerConnection.a(PlayerConnection.java:1102) [minecraft_server.jar:git-Spigot-c3093ef-7e94e65]

at net.minecraft.server.v1_12_R1.NetworkManager.handleDisconnection(NetworkManager.java:321) [minecraft_server.jar:git-Spigot-c3093ef-7e94e65]

at net.minecraft.server.v1_12_R1.ServerConnection.c(ServerConnection.java:174) [minecraft_server.jar:git-Spigot-c3093ef-7e94e65]

at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:845) [minecraft_server.jar:git-Spigot-c3093ef-7e94e65]

at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:406) [minecraft_server.jar:git-Spigot-c3093ef-7e94e65]

at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:679) [minecraft_server.jar:git-Spigot-c3093ef-7e94e65]

at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:577) [minecraft_server.jar:git-Spigot-c3093ef-7e94e65]

at java.lang.Thread.run(Thread.java:748) [?:1.8.0_151]

Caused by: java.util.ConcurrentModificationException

at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:907) ~[?:1.8.0_151]

at java.util.ArrayList$Itr.next(ArrayList.java:857) ~[?:1.8.0_151]

at me.Zrips.TradeMe.PlayerListener.onLogOut(PlayerListener.java:511) ~[?:?]

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_151]

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_151]

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_151]

at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_151]

at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:302) ~[minecraft_server.jar:git-Spigot-c3093ef-7e94e65]

... 12 more