private void removeAllAbilities(Set<Ability> abilities) {
		if (abilities != null) {
			// remove abilities with array loop to avoid concurrentModification exception
			// which will be thrown by the 'removeAbility' method otherwise
			Ability[] array = abilities.toArray(new Ability[abilities.size()]);
			for (int i = 0; i < array.length; ++i) {
				removeAbility(array[i].getOwner(), array[i]);
			}
		}
	}