Sudoku.Sudoku.NextEmpty C# (CSharp) Method

        static int[] NextEmpty(int[,] sudoku)
        {
            for (int i = 0; i < BOARD_SIZE; i++)
            {
                for (int j = 0; j < BOARD_SIZE; j++)
                {
                    if (sudoku[i, j] == 0)
                    {
                        return new int[] { i, j };
                    }
                }
            }
            return null;
        }