public void check() throws InvalidGameStateException {
		if (points == 0) throw new InvalidGameStateException("field '"+answer+"' has no points assigned (=0)");
		if (answer == null || answer.isEmpty()) throw new InvalidGameStateException("field has null or empty string set as an answer");
		if (status == null) throw new InvalidGameStateException("field '"+answer+"' has null as its status");
	}