What does this mean?

[Onyx235]

[13:58:31] [Server thread/ERROR]: Could not pass event EntityDamageByEntityEvent to mcMMO v1.5.04-SNAPSHOT-b${BUILD_NUMBER}
org.bukkit.event.EventException
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:309) ~[StellarSpigot.jar:git-TacoSpigot-04511af6]
at co.aikar.timings.TimedEventExecutor.execute(TimedEventExecutor.java:78) ~[StellarSpigot.jar:git-TacoSpigot-04511af6]
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[StellarSpigot.jar:git-TacoSpigot-04511af6]
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:508) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:493) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at org.bukkit.craftbukkit.v1_8_R3.event.CraftEventFactory.callEvent(CraftEventFactory.java:91) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at org.bukkit.craftbukkit.v1_8_R3.event.CraftEventFactory.callEntityDamageEvent(CraftEventFactory.java:706) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at org.bukkit.craftbukkit.v1_8_R3.event.CraftEventFactory.handleEntityDamageEvent(CraftEventFactory.java:619) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at org.bukkit.craftbukkit.v1_8_R3.event.CraftEventFactory.handleLivingEntityDamageEvent(CraftEventFactory.java:738) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at net.minecraft.server.v1_8_R3.EntityLiving.d(EntityLiving.java:1195) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at net.minecraft.server.v1_8_R3.EntityLiving.damageEntity(EntityLiving.java:807) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at net.minecraft.server.v1_8_R3.EntityMonster.damageEntity(EntityMonster.java:43) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at net.minecraft.server.v1_8_R3.EntityHuman.attack(EntityHuman.java:1010) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at net.minecraft.server.v1_8_R3.EntityPlayer.attack(EntityPlayer.java:1095) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at net.minecraft.server.v1_8_R3.PlayerConnection.a(PlayerConnection.java:1373) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at net.minecraft.server.v1_8_R3.PacketPlayInUseEntity.a(SourceFile:52) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at net.minecraft.server.v1_8_R3.PacketPlayInUseEntity.a(SourceFile:11) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at net.minecraft.server.v1_8_R3.PlayerConnectionUtils$1.run(SourceFile:13) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.8.0_151]
at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.8.0_151]
at net.minecraft.server.v1_8_R3.SystemUtils.a(SourceFile:44) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:809) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:821) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:748) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:649) [StellarSpigot.jar:git-TacoSpigot-04511af6]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_151]
Caused by: java.lang.NullPointerException
at net.minecraft.server.v1_8_R3.World.createExplosion(World.java:2660) ~[StellarSpigot.jar:git-TacoSpigot-04511af6]
at net.minecraft.server.v1_8_R3.WorldServer.createExplosion(WorldServer.java:1090) ~[StellarSpigot.jar:git-TacoSpigot-04511af6]
at org.bukkit.craftbukkit.v1_8_R3.CraftWorld.createExplosion(CraftWorld.java:573) ~[StellarSpigot.jar:git-TacoSpigot-04511af6]
at com.gmail.nossr50.util.skills.ParticleEffectUtils.playGreaterImpactEffect(ParticleEffectUtils.java:71) ~[mcMMO.jar:?]
at com.gmail.nossr50.skills.axes.AxesManager.greaterImpact(AxesManager.java:126) ~[mcMMO.jar:?]
at com.gmail.nossr50.util.skills.CombatUtils.processAxeCombat(CombatUtils.java:101) ~[mcMMO.jar:?]
at com.gmail.nossr50.util.skills.CombatUtils.processCombatAttack(CombatUtils.java:250) ~[mcMMO.jar:?]
at com.gmail.nossr50.listeners.EntityListener.onEntityDamageByEntity(EntityListener.java:238) ~[mcMMO.jar:?]
at sun.reflect.GeneratedMethodAccessor516.invoke(Unknown Source) ~[?:?]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_151]
at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_151]
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:307) ~[StellarSpigot.jar:git-TacoSpigot-04511af6]
... 25 more