I have been working on getting the id of the mob but for some reason when i check to see if the item is null or my item it crashes.

 

@SubscribeEvent
public void OnEntityDeath(LivingDeathEvent event)
{
	if(event.source.getSourceOfDamage() instanceof EntityPlayer)
	{
		EntityPlayer player = (EntityPlayer) event.source.getSourceOfDamage();
		int size = player.inventory.mainInventory.length;
		for(int i = 0; i < size; i++)
		{
			ItemStack itemStack = player.inventory.mainInventory[i];
			if(itemStack.getItem() != null)
			{
				if(itemStack.getItem() instanceof ItemSoulJar)
				{
					//if(rand.nextInt(50) == 1)
						if(itemStack.stackTagCompound == null)
						{
							itemStack.setTagCompound(new NBTTagCompound());
							itemStack.stackTagCompound.setInteger("Entity Id", event.entityLiving.getEntityId());
						}
				}
			}
		}
	}
}

 

---- Minecraft Crash Report ----
// Quite honestly, I wouldn't worry myself about that.

Time: 16/05/14 1:05 AM
Description: Ticking memory connection

java.lang.NullPointerException: Ticking memory connection
at com.jdb.base.events.ModEventHandler.OnEntityDeath(ModEventHandler.java:31)
at cpw.mods.fml.common.eventhandler.ASMEventHandler_4_ModEventHandler_OnEntityDeath_LivingDeathEvent.invoke(.dynamic)
at cpw.mods.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:51)
at cpw.mods.fml.common.eventhandler.EventBus.post(EventBus.java:122)
at net.minecraftforge.common.ForgeHooks.onLivingDeath(ForgeHooks.java:289)
at net.minecraft.entity.EntityLivingBase.onDeath(EntityLivingBase.java:992)
at net.minecraft.entity.passive.EntityHorse.onDeath(EntityHorse.java:1018)
at net.minecraft.entity.EntityLivingBase.attackEntityFrom(EntityLivingBase.java:950)
at net.minecraft.entity.passive.EntityAnimal.attackEntityFrom(EntityAnimal.java:224)
at net.minecraft.entity.passive.EntityHorse.attackEntityFrom(EntityHorse.java:360)
at net.minecraft.entity.player.EntityPlayer.attackTargetEntityWithCurrentItem(EntityPlayer.java:1401)
at net.minecraft.network.NetHandlerPlayServer.processUseEntity(NetHandlerPlayServer.java:873)
at net.minecraft.network.play.client.C02PacketUseEntity.processPacket(C02PacketUseEntity.java:51)
at net.minecraft.network.play.client.C02PacketUseEntity.processPacket(C02PacketUseEntity.java:69)
at net.minecraft.network.NetworkManager.processReceivedPackets(NetworkManager.java:232)
at net.minecraft.network.NetworkSystem.networkTick(NetworkSystem.java:182)
at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:720)
at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:608)
at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:118)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:482)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:746)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
at com.jdb.base.events.ModEventHandler.OnEntityDeath(ModEventHandler.java:31)
at cpw.mods.fml.common.eventhandler.ASMEventHandler_4_ModEventHandler_OnEntityDeath_LivingDeathEvent.invoke(.dynamic)
at cpw.mods.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:51)
at cpw.mods.fml.common.eventhandler.EventBus.post(EventBus.java:122)
at net.minecraftforge.common.ForgeHooks.onLivingDeath(ForgeHooks.java:289)
at net.minecraft.entity.EntityLivingBase.onDeath(EntityLivingBase.java:992)
at net.minecraft.entity.passive.EntityHorse.onDeath(EntityHorse.java:1018)
at net.minecraft.entity.EntityLivingBase.attackEntityFrom(EntityLivingBase.java:950)
at net.minecraft.entity.passive.EntityAnimal.attackEntityFrom(EntityAnimal.java:224)
at net.minecraft.entity.passive.EntityHorse.attackEntityFrom(EntityHorse.java:360)
at net.minecraft.entity.player.EntityPlayer.attackTargetEntityWithCurrentItem(EntityPlayer.java:1401)
at net.minecraft.network.NetHandlerPlayServer.processUseEntity(NetHandlerPlayServer.java:873)
at net.minecraft.network.play.client.C02PacketUseEntity.processPacket(C02PacketUseEntity.java:51)
at net.minecraft.network.play.client.C02PacketUseEntity.processPacket(C02PacketUseEntity.java:69)
at net.minecraft.network.NetworkManager.processReceivedPackets(NetworkManager.java:232)

-- Ticking connection --
Details:
Connection: net.minecraft.network.NetworkManager@71431492
Stacktrace:
at net.minecraft.network.NetworkSystem.networkTick(NetworkSystem.java:182)
at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:720)
at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:608)
at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:118)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:482)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:746)

-- System Details --
Details:
Minecraft Version: 1.7.2
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.7.0_21, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 924929440 bytes (882 MB) / 1056309248 bytes (1007 MB) up to 1056309248 bytes (1007 MB)
JVM Flags: 3 total; -Xincgc -Xmx1024M -Xms1024M
AABB Pool Size: 2688 (150528 bytes; 0 MB) allocated, 2443 (136808 bytes; 0 MB) used
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP v9.03 FML v7.2.196.1082 Minecraft Forge 10.12.1.1082 4 mods loaded, 4 mods active
mcp{9.03} [Minecraft Coder Pack] (minecraft.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
FML{7.2.196.1082} [Forge Mod Loader] (forgeSrc-1.7.2-10.12.1.1082.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Forge{10.12.1.1082} [Minecraft Forge] (forgeSrc-1.7.2-10.12.1.1082.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Totem{1.0} [Totem] (bin) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Profiler Position: N/A (disabled)
Vec3 Pool Size: 339 (18984 bytes; 0 MB) allocated, 314 (17584 bytes; 0 MB) used
Player Count: 1 / 8; [EntityPlayerMP['Player219'/145, l='New World', x=355.91, y=4.00, z=-808.66]]
Type: Integrated Server (map_client.txt)
Is Modded: Definitely; Client brand changed to 'fml,forge'

The ItemStack may also be null, and if it's not, then itemstack.getItem() will not ever be null.

 

"if (itemstack != null && itemstack.getItem() instanceof SomeItem)" is safe from null exceptions.