Extending the NPC model

[xpDad 4]

Hey was wondering if anyone came up with a solution for this. So what I want to do is to extend the NPC model to have my specific methods for it as : 

public class ExtNpc extends NPC {

	public ExtNpc(final NPC reference) {
		super(reference);
	}

	public void attack() {
		interact("Attack");
	}

	public boolean isDead() {
		return getHealthPercent() == 0;
	}

	public boolean isUnderAttack(final Character character) {
		return !character.isInteracting(this);
	}

}

but the problem is that it doesn't work as supposed and throws null pointers at times or has bad reference. Any ideas on this?

[camelCase 257]

why do this in the first place? you are adding complexity to save like .5 seconds typing

[xpDad 4]

Well I believe that doing so will help save some time in the future and have a single point of access to do specific action which would help me to refactor or introduce new logic if needed.