序列在c＃中不包含元素

Question

private void dataGridView1_SelectionChanged(object sender, EventArgs e)
{
     DataGridView dg = sender as DataGridView;
     if (dg != null && dg.SelectedRows.Count > 0)
     {
         DataGridViewRow row = dg.SelectedRows[0];
         if (row != null)
         {
             textBox1.Text = row.Cells[0].Value.ToString();
             textBox2.Text = row.Cells[1].Value.ToString();
             textBox3.Text = row.Cells[2].Value.ToString();
             comboBox10.Text = row.Cells[3].Value.ToString();
             dateTimePicker1.Text = row.Cells[4].Value.ToString();

             var buletinID = (int)row.Cells[15].Value;
             var dateBuletin = db.Buletin.Where(i => i.ID == buletinID + 1).First();
             textBox16.Text = dateBuletin.Seria.ToString();
             textBox17.Text = dateBuletin.Numarul.ToString();
             textBox18.Text = dateBuletin.Eliberat_de_oficiul.ToString();
             dateTimePicker3.Text = dateBuletin.Data_eliberarii.ToString();

             var livretID = (int)row.Cells[16].Value; 
             if (livretID != null)
             {

                 // This is the line that throws.
                 var dateLivret = db.Livret_militar.Where(i => i.ID == livretID).First(); 

                 textBox22.Text = dateLivret.Seria.ToString();
                 textBox23.Text = dateLivret.Numarul.ToString();
                 comboBox5.Text = dateLivret.Da_sau_Nu.ToString();
                 groupBox1.Controls.OfType<RadioButton>().Where(c => c.Text == dateLivret.Evidenta.ToString()).FirstOrDefault().Checked = true;
             }

我在textboxes，combobox，datetimepicker，单选按钮组中使用datagridview显示文本。当我选择一行时，文本显示在空框中。