Cannot set the SelectedValue in a ListControl with an empty ValueMember in winform using c#

I have a combobox that loads data from database but i got an error that you cannot set the selectedValue in a ListControl Although i have set the selectValue to a Primary key of a Table. But still getting error on runtime.. Here is the Code.. ``` private void FormAddStudent_Load(object sender, EventArgs e) { //For combobox Campuse cBoxCampus.DataSource = GetAllCampuses(); cBoxCampus.DisplayMember = "campus_name"; cBoxCampus.SelectedValue = "campus_id"; //Foe ComboBox Department cBoxDepartment.DataSource = GetAllDepartment(); cBoxDepartment.DisplayMember = "depname"; cBoxDepartment.SelectedValue = "depid"; } ``` and this is the code behind Insert Button ``` private void btnInsert_Click(object sender, EventArgs e) { string CS = ConfigurationManager.ConnectionStrings["UMSdbConnectionString"].ConnectionString; using (SqlConnection con = new SqlConnection(CS)) { con.Open(); SqlCommand cmd = new SqlCommand("SELECT ISNULL(MAX(std_id),0)+1 FROM Student", con); cmd.CommandType = CommandType.Text; tbID.Text = cmd.ExecuteScalar().ToString(); { using (SqlCommand cmd1 = new SqlCommand("INSERT INTO Student (std_id,std_name,std_f_name,std_mob,std_gender,std_cnic,std_campus,std_dep,std_address,std_batch,std_batch_year)VALUES(@std_id,@std_name,@std_f_name,@std_mob,@std_gender,@std_cnic,@std_campus,@std_dep,@std_address,@std_batch,@std_batch_year)VALUES(@campus_id,@campus_name)", con)) { cmd1.CommandType = CommandType.Text; cmd1.Parameters.AddWithValue("@std_id", tbID.Text); cmd1.Parameters.AddWithValue("@std_name", tbName.Text); cmd1.Parameters.AddWithValue("@std_f_name", tbFatherName.Text); cmd1.Parameters.AddWithValue("@std_mob", tbMobNumber.Text); cmd1.Parameters.AddWithValue("@std_gender", GetGender()); cmd1.Parameters.AddWithValue("@std_cnic", tbMobNumber.Text); cmd1.Parameters.AddWithValue("@std_campus",(cBoxCampus.SelectedIndex == -1) ? 0: cBoxCampus.SelectedValue); cmd1.Parameters.AddWithValue("@std_dep", (cBoxDepartment.SelectedIndex == -1) ? 0 : cBoxDepartment.SelectedValue); cmd1.Parameters.AddWithValue("@std_address", tbAddress.Text); cmd1.Parameters.AddWithValue("@std_batch", tbBatchNo.Text); cmd1.Parameters.AddWithValue("@std_batch_year", tbBatchYear.Text); cmd1.ExecuteNonQuery(); con.Close(); MessageBox.Show("Record Saved"); } } } } ```