How to insert a null value to combobox which is bind with datasource

Question

Hi,
i am working on c# winforms application. I have 2 comboboxes one is CustomerCbBox and another is OrderCbBox. CustomerCbBox is bind with data source.
on CustomerCbBox SelectedIndexChanged event data is populated in OrderCbBox from data source. 
i want to add a null or empty field in CustomerCbBox. all I want is that when the user don't Select Customer Name and OrderNo null or empty data enter in database. but when i click Insert Button it generate error "Object reference is not "object
reference not set to an instance of an object".
here is my code.
  private void MainForm_Load(object sender, EventArgs e)
production pd = new production();
CustomerCbBox.DataSource = pd.Customer();
CustomerCbBox.DisplayMember = "Cust";
CustomerCbBox.ValueMember = "CustId";
 private void CustomerCbBox_SelectedIndexChanged(object sender, EventArgs e)
                  try
                      string PartyName = CustomerCbBox.SelectedIndex.ToString();
                       PONum1.DataSource = pd.GetPOnumActive(PartyName1);
                          PONum1.DisplayMember = "PONum";
                          PONum1.ValueMember = "PONum";
                  catch (Exception ex)
                      MessageBox.Show(ex.Message);
     Please help me to solve this problem thanks.      

Answer 1

Hello,
We could check whether the user has selected any items before adding that to database.
if (CustomerCbBox.SelectedIndex > -1)
// do something
}else{//add dbnull to database}
And for adding null to databse, we could pass DBNull.Value instead.
Regards,
Carl
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