from typing import List
from typing import Union
from typing import Tuple


def find_empty(b : List[List[int]]) -> Union[Tuple[int, int], None]:
    """Finds the empty cell in sudoku

    Parameters:
        b(List[List[int]]) :  List of List that represents a sudoku board

    Returns:
        (i, j)(Tuple(i, j)) : index of empty cell

    """
    for i in range(len(b)):
        for j in range(len(b[0])):
            if b[i][j] == 0:
                return (i, j)  # row, col

    return None