I created a database and wrote functions that should take column names from tables and put them in DataGridViewComboBoxCells. However, after running the program, no errors came out, but all ComboBoxCells are empty

I created a function that accesses the database, takes the column names from there and returns a dictionary:

public Dictionary<int, List<string>> GetDisciplinesHeaders(string connectionString, string tableName)
        {
            Dictionary<int, List<string>> headers = new Dictionary<int, List<string>>();
            try
            {
                using (OleDbConnection connection = new OleDbConnection(connectionString))
                {
                    connection.Open();
                    string query = $"SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = '{tableName}' AND COLUMN_NAME != 'Class'";
                    using (OleDbCommand command = new OleDbCommand(query, connection))
                    {
                        using (OleDbDataReader reader = command.ExecuteReader())
                        {
                            int classNumber = 1; // Начинаем с первого класса
                            while (reader.Read())
                            {
                                if (!headers.ContainsKey(classNumber)) { 
                                    headers[classNumber] = new List<string>();
                                }

                                headers[classNumber].Add(reader.GetString(0));
                                classNumber++;

                            }
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine("Ошибка: " + ex.Message);
            }

            return headers;
        }

Created a function that renders a DataGridView with a Datagridviewcomboboxcell inside:

private DataGridView CreateDataGridView()
        {
            DataGridView dataGridView = new DataGridView();
            dataGridView.Dock = DockStyle.Fill;

            DataGridViewTextBoxColumn rowNumerColumn = new DataGridViewTextBoxColumn();
            rowNumerColumn.HeaderText = "#";
            dataGridView.Columns.Add(rowNumerColumn);


            for (int i = 0; i < 12; i++)
            {
                if (i % 2 == 0)
                {
                    DataGridViewComboBoxColumn subjectColumn = new DataGridViewComboBoxColumn();
                    subjectColumn.HeaderText = $"Класс {i / 2 + 1} Дисциплины";
                    dataGridView.Columns.Add(subjectColumn);

                    // Проверяем номер класса и выбираем соответствующую таблицу
                    string tableName;
                    if (i + 1 >= 1 && i + 1 <= 4)
                        tableName = "Disciplines1_4";
                    else if (i + 1 >= 5 && i + 1 <= 9)
                        tableName = "Disciplines5_9";
                    else
                        tableName = "Disciplines10_11";

                    // Получаем названия полей из таблицы и заполняем ComboBox
                    Dictionary<int, List<string>> headers = GetDisciplinesHeaders(connectString, tableName);
                    if (headers.ContainsKey(i / 2 + 1))
                    {
                        foreach (string header in headers[i / 2 + 1])
                        {
                            subjectColumn.Items.Add(header);
                        }
                    }
                }
                else
                {
                    DataGridViewTextBoxColumn roomColumn = new DataGridViewTextBoxColumn();
                    roomColumn.HeaderText = "кабинет";
                    dataGridView.Columns.Add(roomColumn);
                }
            }

            // Остальной код обработки событий и т.д.

            return dataGridView;
        }