MMM Error

15:30:08 [SEVERE] Could not pass event EntityDeathEvent to mobmakemoney v1.3
org.bukkit.event.EventException
        at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.ja
va:427)
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.jav
a:62)
        at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.j
ava:477)
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.j
ava:462)
        at org.bukkit.craftbukkit.v1_6_R2.event.CraftEventFactory.callEntityDeat
hEvent(CraftEventFactory.java:327)
        at net.minecraft.server.v1_6_R2.EntityInsentient.dropDeathLoot(EntityIns
entient.java:202)
        at net.minecraft.server.v1_6_R2.EntityLiving.die(EntityLiving.java:757)
        at net.minecraft.server.v1_6_R2.EntityHorse.die(EntityHorse.java:701)
        at net.minecraft.server.v1_6_R2.EntityLiving.damageEntity(EntityLiving.j
ava:709)
        at net.minecraft.server.v1_6_R2.EntityAnimal.damageEntity(SourceFile:128
)
        at net.minecraft.server.v1_6_R2.EntityHorse.damageEntity(EntityHorse.jav
a:251)
        at net.minecraft.server.v1_6_R2.EntityHuman.attack(EntityHuman.java:884)

        at net.minecraft.server.v1_6_R2.PlayerConnection.a(PlayerConnection.java
:1121)
        at net.minecraft.server.v1_6_R2.Packet7UseEntity.handle(SourceFile:36)
        at net.minecraft.server.v1_6_R2.Packet7UseEntity$$EnhancerByCGLIB$$9b1bd
5fd.CGLIB$handle$0(<generated>)
        at net.minecraft.server.v1_6_R2.Packet7UseEntity$$EnhancerByCGLIB$$9b1bd
5fd$$FastClassByCGLIB$$82b4109a.invoke(<generated>)
        at com.comphenix.net.sf.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.
java:228)
        at com.comphenix.protocol.injector.packet.ReadPacketModifier.intercept(R
eadPacketModifier.java:116)
        at net.minecraft.server.v1_6_R2.Packet7UseEntity$$EnhancerByCGLIB$$9b1bd
5fd.handle(<generated>)
        at net.minecraft.server.v1_6_R2.NetworkManager.b(NetworkManager.java:296
)
        at net.minecraft.server.v1_6_R2.PlayerConnection.e(PlayerConnection.java
:116)
        at net.minecraft.server.v1_6_R2.ServerConnection.b(SourceFile:37)
        at net.minecraft.server.v1_6_R2.DedicatedServerConnection.b(SourceFile:3
0)
        at net.minecraft.server.v1_6_R2.MinecraftServer.t(MinecraftServer.java:5
90)
        at net.minecraft.server.v1_6_R2.DedicatedServer.t(DedicatedServer.java:2
26)
        at net.minecraft.server.v1_6_R2.MinecraftServer.s(MinecraftServer.java:4
86)
        at net.minecraft.server.v1_6_R2.MinecraftServer.run(MinecraftServer.java
:419)
        at net.minecraft.server.v1_6_R2.ThreadServerApplication.run(SourceFile:5
82)
Caused by: java.lang.NullPointerException
        at io.github.rawiwut.mobmakemoney.killmob.killmob(killmob.java:37)
        at sun.reflect.GeneratedMethodAccessor75.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.ja
va:425)
        ... 27 more