Calculates board from flop, turn and river.

def board(self):
        """Calculates board from flop, turn and river."""
        board = []
        if self.flop:
            board.extend(self.flop.cards)
            if self.turn:
                board.append(self.turn)
                if self.river:
                    board.append(self.river)
        return tuple(board) if board else None