java.lang.NullPointerException: Ticking entity
at net.minecraft.entity.ai.EntityLookHelper.func_75651_a(SourceFile:18)
at net.minecraft.entity.ai.EntityAIAttackOnCollide.func_75246_d(EntityAIAttackOnCollide.java:93)
at net.minecraft.entity.ai.EntityAITasks.func_75774_a(SourceFile:103)
at net.minecraft.entity.EntityLiving.func_70619_bc(EntityLiving.java:540)
at net.minecraft.entity.EntityLivingBase.func_70636_d(EntityLivingBase.java:1774)
at net.minecraft.entity.EntityLiving.func_70636_d(EntityLiving.java:367)
at net.minecraft.entity.monster.EntityMob.func_70636_d(SourceFile:25)
at net.minecraft.entity.monster.EntityZombie.func_70636_d(EntityZombie.java:217)
at net.minecraft.entity.EntityLivingBase.func_70071_h_(EntityLivingBase.java:1611)
at net.minecraft.entity.EntityLiving.func_70071_h_(EntityLiving.java:206)
at net.minecraft.entity.monster.EntityMob.func_70071_h_(SourceFile:30)
at net.minecraft.entity.monster.EntityZombie.func_70071_h_(EntityZombie.java:303)
at net.minecraft.world.World.func_72866_a(World.java:2070)
at net.minecraft.world.WorldServer.func_72866_a(WorldServer.java:648)
at net.minecraft.world.World.func_72870_g(World.java:2034)
at net.minecraft.world.World.func_72939_s(World.java:1887)
at net.minecraft.world.WorldServer.func_72939_s(WorldServer.java:489)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:636)
at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:334)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:547)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:396)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685)