code: public PlayerGuessResult displayNextCard(RelationshipToPreviousCard guess) {
      Card card = deck.turnCard();
      grid.nextCard(card);
      cardsTurnedPlusOne++;
  
      RelationshipToPreviousCard actualRelationshipToPrevious = getRelationshipToPreviousCard(card);
      previous = card;
      if (actualRelationshipToPrevious == null) {
        return null;
      }
  
      return actualRelationshipToPrevious.equals(guess) ? PlayerGuessResult.RIGHT : PlayerGuessResult.WRONG;
    }
docs: Turn the next card.
  @param guess the player's guess
  @return whether the player was right or wrong