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[1.7.10] [Solved] Potion#performEffect leads to Null Pointer Error?


IceMetalPunk

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I have a fluid block that, when the player touches it, should give them random status effects until they stop touching it. However, upon colliding with the block, it instead crashes the game with a Null Pointer Error. Which I can't figure out, because if I comment out just the line that calls Potion#performEffect, there are no crashes or errors, but some debug output confirms that the potion instance and the player are both not null, so what could possibly be null?

 

Here's the code:

 

	public void onEntityCollidedWithBlock(World world, int x, int y, int z, Entity ent) {
	if (world.isRemote || ent == null || !(ent instanceof EntityLivingBase)) {
		return;
	}
	EntityLivingBase player = (EntityLivingBase) ent;
	int potID = world.rand.nextInt(Potion.potionTypes.length);
	Potion pot = Potion.potionTypes[potID];
	System.out.println("Potion " + pot + ", Player " + player); // Debug output
	pot.performEffect(player, 0);
}

 

If I comment out just that last line, the crash doesn't happen, but of course no status effects are applied. Just before the crash, it outputs the debug message showing that "pot" is an instance of Potion, and "player" is an instance of EntityPlayerMP. So where's the null value here?

 

(Note: I'm not 100% sure what the second parameter to performEffect is; it looks like it's the level, so I put 0 for level 1, but I also tried with 40 on the guess it might actually be tick duration; that crashed just the same.)

Whatever Minecraft needs, it is most likely not yet another tool tier.

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You can either step into the call using the debugger or post (in spoiler tags) the crash report.

The debugger is a powerful and necessary tool in any IDE, so learn how to use it. You'll be able to tell us more and get better help here if you investigate your runtime problems in the debugger before posting.

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Also, some potion effects will be utterly harmless when you tick them once (poison, hunger, slowness, weakness, fatigue, wither) while others will be super deadly (instant damage).

Apparently I'm a complete and utter jerk and come to this forum just like to make fun of people, be confrontational, and make your personal life miserable.  If you think this is the case, JUST REPORT ME.  Otherwise you're just going to get reported when you reply to my posts and point it out, because odds are, I was trying to be nice.

 

Exception: If you do not understand Java, I WILL NOT HELP YOU and your thread will get locked.

 

DO NOT PM ME WITH PROBLEMS. No help will be given.

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Not all potionIDs are valid. You need to check if there is a potion with that ID before you use it. What I mean is: Potion.potionTypes it not completely filled with potions, there are null entries for IDs that do not exist.

 

>_< D'oh! That seems to have solved the problem. Apparently, when it was crashing, it wasn't even outputting the null potion in the debug message first for some reason. I just added a check to return if pot==null, and it works. Go figure. Thank you!

 

Also, some potion effects will be utterly harmless when you tick them once (poison, hunger, slowness, weakness, fatigue, wither) while others will be super deadly (instant damage).

 

Yes, balancing will be done through a whitelist/blacklist of effects. I just haven't yet determined which effects should stay and which should go yet; that'll be future work. I'm probably going to end up using addPotionEffect instead after all, but I'm still glad I made this topic because without the explicit check for null potions, it'd still have had this same problem.

 

Thanks, everyone! :)

Whatever Minecraft needs, it is most likely not yet another tool tier.

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