Error : invalid attempt to read when no data is present

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C#

Hi,

I want to connect the data base for creating and backup data. when I try to connect the data base it gives me an error Invalid attempt to read when no data is present.

Please help me on this.

What I have tried:

 public partial class Backup_or_Restore_Data : Form
    {
        private SqlConnection con;
        private SqlCommand command;
        private SqlDataReader reader;
        string sql = "";
        string connectionString = "";
private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                connectionString = "Data Source = " + textBox1.Text + "; User Id = " + textBox2.Text + "; Password = " + textBox3.Text + "";
                con = new SqlConnection(connectionString);
                con.Open();
                sql = "EXEC sp_databases";
                command = new SqlCommand(sql, con);
                reader = command.ExecuteReader();
                comboBox1.Items.Clear();
                while (reader.Read());
                {
                    comboBox1.Items.Add(reader[0].ToString());

                }

            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

        }
    }