C#

string authors = string.Join(", ", md.Author??new string[] {"<NN>"});

if (md.Author != null)
{
    string[] authors = md.Author;
    // process the author details
} 
else
{
    // n author details
}

string authors = string.Join(", ", md.Author.AsEnumerable() ?? Array.Empty<string>());

Function MakeList( _
    ByVal InSQL As String, _
    Optional ByVal InColName = 0, _
    Optional ByVal InSeparator As String = ",", _
    Optional ByVal InDataBase = "" _
    ) As String
    ' Convert a column from a table into a list
    '
    ' Parameters
    '   InSQL       SQL query
    '   InColName   Optional. Column containing data to be converted to a list
    '               (either by column number or by name)
    '   InSeparator Optional. Text to separate list items
    '   InDataBase  Optional. Database to find. Can be name (string) or
    '               database object. Current DB assumed if not specified
    '
    ' Result
    '   List of data
 
    Dim DB As Database
    Dim rs ' As Recordset
    
    ' Open the recordset
    If IsObject(InDataBase) Then
        Set DB = InDataBase
    Else
        Set DB = IIf(InDataBase = "", CurrentDb, OpenDatabase(InDataBase))
    End If
    
    Set rs = DB.OpenRecordset(InSQL)
    ' rs.MoveFirst
    While Not rs.EOF
        MakeList = MakeList & InSeparator & rs(InColName)
        rs.MoveNext
    Wend
    
    ' Get the data
    rs.Close
    DB.Close
    
    MakeList = Mid(MakeList, Len(InSeparator) + 1)  ' Drop first ','
End Function    ' MakeList

<button type="submit" formaction="login?expire=1" class="btn btn-ic btn-link pkg-photo">Olvide mi clave</button>

Super Lloyd wrote:

luckily there is a common entry point

// in Form1
// after you create a new instance of Form2
Form2 f2 = new Form2();
// add the handler
f2.AddCreditorName += UpdateComboBox;

public void UpdateComboBox(string newCreditorName)
{
     // add validation here ? check for duplicate names ?
     comboBox1.Items.Add(newCreditorName);
}

// in Form2

// public delegate takes one parameter of type 'string and returns void
public Action<string> AddCreditorName = null;

// when Form2 is complete ... all the information is entered/validated
// in the Click handler for Form2's 'Save button
if (AddCreditorName != null) AddCreditorName(CreditorNamtmeTextBox.Text);

void CreditorDataLoad()
        {
            try
            {
                cbo_BillName.Items.Clear();

                string query = "select C_Name From Creditor";

                AC.cmd.Parameters.Clear();
                AC.cmd.CommandType = CommandType.Text;
                AC.cmd.CommandText = query;

                AC.openConnection();
                AC.rd = AC.cmd.ExecuteReader();

                if (AC.rd.HasRows)
                {
                    while (AC.rd.Read())
                    {
                        cbo_BillName.Items.Add(AC.rd[0].ToString());
                    }

                }
                AC.rd.Close();
                AC.closeConnection();
            }
            catch (Exception ex)
            {
                MessageBox.Show("Error" + ex);
            }
        }

private void btnNewBill_Click(object sender, EventArgs e)
        {
            billName = null;
            this.Hide();

            creditEditor f2 = new creditEditor(this);


            f2.FormClosed += new FormClosedEventHandler(creditEditor_FormClosed);
            f2.ShowDialog();

        }
        void creditEditor_FormClosed(object sender, EventArgs e)
        {

            CreditorDataLoad();

        }