[SEVERE] Could not pass event EntityDamageByEntityEvent to WeaponLevels v1.2.6
org.bukkit.event.EventException
	at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:427)
	at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
	at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:477)
	at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:462)
	at org.bukkit.craftbukkit.v1_6_R3.event.CraftEventFactory.callEvent(CraftEventFactory.java:93)
	at org.bukkit.craftbukkit.v1_6_R3.event.CraftEventFactory.callEntityDamageEvent(CraftEventFactory.java:381)
	at org.bukkit.craftbukkit.v1_6_R3.event.CraftEventFactory.handleEntityDamageEvent(CraftEventFactory.java:406)
	at net.minecraft.server.v1_6_R3.EntityLiving.damageEntity(EntityLiving.java:637)
	at net.minecraft.server.v1_6_R3.EntityArrow.l_(EntityArrow.java:229)
	at net.minecraft.server.v1_6_R3.World.entityJoinedWorld(World.java:1354)
	at net.minecraft.server.v1_6_R3.World.playerJoinedWorld(World.java:1335)
	at net.minecraft.server.v1_6_R3.World.tickEntities(World.java:1223)
	at net.minecraft.server.v1_6_R3.WorldServer.tickEntities(WorldServer.java:480)
	at net.minecraft.server.v1_6_R3.MinecraftServer.t(MinecraftServer.java:574)
	at net.minecraft.server.v1_6_R3.DedicatedServer.t(DedicatedServer.java:227)
	at net.minecraft.server.v1_6_R3.MinecraftServer.s(MinecraftServer.java:488)
	at net.minecraft.server.v1_6_R3.MinecraftServer.run(MinecraftServer.java:421)
	at net.minecraft.server.v1_6_R3.ThreadServerApplication.run(SourceFile:583)
Caused by: java.lang.IllegalArgumentException: Cannot add null enchantment
	at org.apache.commons.lang.Validate.notNull(Validate.java:203)
	at org.bukkit.craftbukkit.v1_6_R3.inventory.CraftItemStack.addUnsafeEnchantment(CraftItemStack.java:164)
	at com.coffeecup.novus.weaponlevels.data.LevelEnchantment.apply(LevelEnchantment.java:25)
	at com.coffeecup.novus.weaponlevels.stages.Stage.apply(Stage.java:82)
	at com.coffeecup.novus.weaponlevels.data.LevelData.update(LevelData.java:205)
	at com.coffeecup.novus.weaponlevels.data.LevelData.addExperience(LevelData.java:111)
	at com.coffeecup.novus.weaponlevels.Events.onDamage(Events.java:158)
	at sun.reflect.GeneratedMethodAccessor16.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:425)
	... 17 more