How to make mob immune to certain effect/damage type (SOLVED)

Something like this

I have not tested it but it should work

This doesn't work for some things, as it deals damage once then gets removed since this procedure has a delay with respect to the poison applying its damage. 

Instead, if you're not afraid to code, you may want to try this: click the Edit Code button on the left with your Entity element selected, then go to <YourEntity>Entity.java, then scroll a bit down and below any brackets (just not inside any functions) paste the @Override thing there and the import stuff at the very top of everything in the file. Save and lock code. Make sure to do everything else about the entity before you make this change (if you're wondering, this is how Minecraft handles poison on spiders).

import net.minecraft.world.effect.MobEffectInstance;
import net.minecraft.world.effect.MobEffects;
import net.minecraft.world.effect.MobEffect;

@Override
	public boolean canBeAffected(MobEffectInstance effect)
	{
		 if (!return effect.getEffect() == MobEffects.POISON)
		 {
		 	super.canBeAffected(effect);
		 }
	}

Wait it's wrong and I can't edit it?? Get rid of the word "return" there

@Override
	public boolean canBeAffected(MobEffectInstance effect)
	{
		 if (!effect.getEffect() == MobEffects.POISON)
		 {
		 	super.canBeAffected(effect);
		 }
	}

I dont understand how this is solved also where da heck do i find the AND block ive looked everywhere