private Box nextEmptyBox(char[][] board, int row, int column) {
        int i = row;
        int j = column;
        for (; i < 9; i++) {
            for (; j < 9; j++) {
                if (board[i][j] == '.')
                    return new Box(i, j);
            }
            j = 0;
        }
        return done;
    }