[13:59:38] [Server thread/ERROR]: Could not pass event EntityDamageByEntityEvent to Skills v13.0.0
org.bukkit.event.EventException: null
        at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:320) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:70) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:529) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:514) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at org.bukkit.craftbukkit.v1_14_R1.event.CraftEventFactory.callEvent(CraftEventFactory.java:229) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at org.bukkit.craftbukkit.v1_14_R1.event.CraftEventFactory.callEntityDamageEvent(CraftEventFactory.java:918) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at org.bukkit.craftbukkit.v1_14_R1.event.CraftEventFactory.handleEntityDamageEvent(CraftEventFactory.java:805) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at org.bukkit.craftbukkit.v1_14_R1.event.CraftEventFactory.handleEntityDamageEvent(CraftEventFactory.java:761) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at org.bukkit.craftbukkit.v1_14_R1.event.CraftEventFactory.handleLivingEntityDamageEvent(CraftEventFactory.java:950) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at net.minecraft.server.v1_14_R1.EntityLiving.damageEntity0(EntityLiving.java:1620) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at net.minecraft.server.v1_14_R1.EntityLiving.damageEntity(EntityLiving.java:1073) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at net.minecraft.server.v1_14_R1.EntityArrow.a(EntityArrow.java:365) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at net.minecraft.server.v1_14_R1.EntityArrow.a(EntityArrow.java:277) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at net.minecraft.server.v1_14_R1.EntityArrow.tick(EntityArrow.java:188) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at net.minecraft.server.v1_14_R1.EntityTippedArrow.tick(EntityTippedArrow.java:87) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at net.minecraft.server.v1_14_R1.WorldServer.entityJoinedWorld(WorldServer.java:568) ~[spigot.jar:git-Spigot-94af569-7deb372]
        at net.minecraft.server.v1_14_R1.World.a(World.java:745) [spigot.jar:git-Spigot-94af569-7deb372]
        at net.minecraft.server.v1_14_R1.WorldServer.doTick(WorldServer.java:344) [spigot.jar:git-Spigot-94af569-7deb372]
        at net.minecraft.server.v1_14_R1.MinecraftServer.b(MinecraftServer.java:1068) [spigot.jar:git-Spigot-94af569-7deb372]
        at net.minecraft.server.v1_14_R1.DedicatedServer.b(DedicatedServer.java:393) [spigot.jar:git-Spigot-94af569-7deb372]
        at net.minecraft.server.v1_14_R1.MinecraftServer.a(MinecraftServer.java:970) [spigot.jar:git-Spigot-94af569-7deb372]
        at net.minecraft.server.v1_14_R1.MinecraftServer.run(MinecraftServer.java:815) [spigot.jar:git-Spigot-94af569-7deb372]
        at java.lang.Thread.run(Unknown Source) [?:1.8.0_231]
Caused by: java.lang.UnsupportedOperationException
        at java.util.Collections$UnmodifiableCollection.remove(Unknown Source) ~[?:1.8.0_231]
        at org.skills.services.manager.ServiceHandler.canFight(ServiceHandler.java:90) ~[?:?]
        at org.skills.abilities.arbalist.ArbalistBarbedArrow.onAttack(ArbalistBarbedArrow.java:28) ~[?:?]
        at sun.reflect.GeneratedMethodAccessor150.invoke(Unknown Source) ~[?:?]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_231]
        at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_231]
        at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:316) ~[spigot.jar:git-Spigot-94af569-7deb372]
        ... 22 more