I've been trying to write a event where the player will get potion effects after he/she reaches a certain level. At first it worked, I was granted the water breathing effect after reaching level 10 but when I attempt to re-log into the test world I get this crash log.

---- Minecraft Crash Report ----
// You should try our sister game, Minceraft!

Time: 7/26/14 6:45 PM
Description: Ticking memory connection

java.lang.NullPointerException: Ticking memory connection
at cpw.mods.fml.common.network.internal.FMLProxyPacket.processPacket(FMLProxyPacket.java:101)
at net.minecraft.network.NetworkManager.processReceivedPackets(NetworkManager.java:212)
at net.minecraft.network.NetworkSystem.networkTick(NetworkSystem.java:165)
at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:659)
at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:547)
at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:111)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:427)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685)


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

-- Head --
Stacktrace:
at cpw.mods.fml.common.network.internal.FMLProxyPacket.processPacket(FMLProxyPacket.java:101)
at net.minecraft.network.NetworkManager.processReceivedPackets(NetworkManager.java:212)

-- Ticking connection --
Details:
Connection: net.minecraft.network.NetworkManager@59d3789f
Stacktrace:
at net.minecraft.network.NetworkSystem.networkTick(NetworkSystem.java:165)
at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:659)
at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:547)
at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:111)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:427)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685)

-- System Details --
Details:
Minecraft Version: 1.7.10
Operating System: Windows 8.1 (amd64) version 6.3
Java Version: 1.7.0_60, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 723101208 bytes (689 MB) / 1037959168 bytes (989 MB) up to 1037959168 bytes (989 MB)
JVM Flags: 3 total; -Xincgc -Xmx1024M -Xms1024M
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
FML: MCP v9.05 FML v7.10.18.1180 Minecraft Forge 10.13.0.1180 4 mods loaded, 4 mods active
mcp{9.05} [Minecraft Coder Pack] (minecraft.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
FML{7.10.18.1180} [Forge Mod Loader] (forgeBin-1.7.10-10.13.0.1180.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Forge{10.13.0.1180} [Minecraft Forge] (forgeBin-1.7.10-10.13.0.1180.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
RPG Intergation{1.0} [RPG Intergation] (bin) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Profiler Position: N/A (disabled)
Vec3 Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Player Count: 0 / 8; []
Type: Integrated Server (map_client.txt)
Is Modded: Definitely; Client brand changed to 'fml,forge'

 

I suspect that I had missed a step when using the addPotionEffect() method as I rechecked my code and found that the world won't crash if I remove the addPotionEffect() before launching Minecraft in debug mode and add it back in after the world loads, the event would fire smoothly with no crashes.

Was there anything I missed when using addPotionEffect()?

Main Class:

public class RPG {

 public static final String MODID = "RPG Intergation";
 public static final String VERSION = "1.0";

 @EventHandler
         //I had tried FMLInitialization and FMLPostInitialization but to no luck, the world would still crash
 public void Preinit(FMLPreInitializationEvent forge)
    {

	    FMLLog.info("[RPG] Loading Events");
	   
	    MinecraftForge.EVENT_BUS.register(new PlayerEvents());	

		FMLLog.info("[RPG] Events Loaded");
    }

 

Event Class:

public class PlayerEvents {
int tierI = 10;
int tierII = 30;
int tierIII = 50;
int tierIV = 100;

@SubscribeEvent
public void xpBonus(PlayerEvent event){
int playerXP = event.entityPlayer.experienceLevel;
if(playerXP >= tierI){		
	event.entityPlayer.addPotionEffect(new PotionEffect(Potion.waterBreathing.id, 10, 0));		
 }
  
   }

}

I knew that PlayerEvents was not the best choice, at that time I didn't find/know of any better event so I went on to use it...

PlayerTickEvent works, thanks