ZA error

2013-07-23 14:32:52 [SEVERE] Could not pass event EntityDamageByEntityEvent to ZArena v0.7.3
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_R2.event.CraftEventFactory.callEvent(CraftEventFactory.java:95)
	at org.bukkit.craftbukkit.v1_6_R2.event.CraftEventFactory.callEntityDamageEvent(CraftEventFactory.java:383)
	at org.bukkit.craftbukkit.v1_6_R2.event.CraftEventFactory.handleEntityDamageEvent(CraftEventFactory.java:408)
	at net.minecraft.server.v1_6_R2.EntityLiving.damageEntity(EntityLiving.java:614)
	at net.minecraft.server.v1_6_R2.EntityMonster.damageEntity(EntityMonster.java:39)
	at net.minecraft.server.v1_6_R2.EntityArrow.l_(EntityArrow.java:229)
	at net.minecraft.server.v1_6_R2.World.entityJoinedWorld(World.java:1354)
	at net.minecraft.server.v1_6_R2.World.playerJoinedWorld(World.java:1335)
	at net.minecraft.server.v1_6_R2.World.tickEntities(World.java:1223)
	at net.minecraft.server.v1_6_R2.WorldServer.tickEntities(WorldServer.java:480)
	at net.minecraft.server.v1_6_R2.MinecraftServer.t(MinecraftServer.java:572)
	at net.minecraft.server.v1_6_R2.DedicatedServer.t(DedicatedServer.java:226)
	at net.minecraft.server.v1_6_R2.MinecraftServer.s(MinecraftServer.java:486)
	at net.minecraft.server.v1_6_R2.MinecraftServer.run(MinecraftServer.java:419)
	at net.minecraft.server.v1_6_R2.ThreadServerApplication.run(SourceFile:582)
Caused by: java.lang.NullPointerException
	at com.github.customentitylibrary.entities.CustomEntityWrapper.instanceOf(CustomEntityWrapper.java:262)
	at com.github.zarena.WaveHandler.onEntityDamageByEntity(WaveHandler.java:421)
	at sun.reflect.GeneratedMethodAccessor74.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:425)
	... 18 more