How to prevent exception when updating the gridview?

protected void Grid_Updating(object sender, GridViewUpdateEventArgs e) 
    { 
        SqlCommand cmd = DataProvider.GenerateCommand("Update_HowzeEducation_SP", CommandType.StoredProcedure); 
        cmd.Connection.Open(); 
 
        cmd.Parameters.Add("@FieldName", SqlDbType.NVarChar).Value = ((TextBox)GridView1.Rows[e.RowIndex].Cells[1].Controls[0]).Text; 
        cmd.Parameters.Add("@DegreeId", SqlDbType.Int).Value = ((TextBox)GridView1.Rows[e.RowIndex].Cells[2].Controls[0]).Text; 
        cmd.Parameters.Add("@SchoolName", SqlDbType.NVarChar).Value = ((TextBox)GridView1.Rows[e.RowIndex].Cells[3].Controls[0]).Text; 
        cmd.Parameters.Add("@StudyCityDescribtion", SqlDbType.NVarChar).Value = ((TextBox)GridView1.Rows[e.RowIndex].Cells[4].Controls[0]).Text; 
        cmd.Parameters.Add("@Average", SqlDbType.Decimal).Value = decimal.Parse(((TextBox)GridView1.Rows[e.RowIndex].Cells[5].Controls[0]).Text, CultureInfo.InvariantCulture); 
        cmd.Parameters.Add("@FinishLevelDate", SqlDbType.Date).Value = Convert.ToDateTime(((TextBox)GridView1.Rows[e.RowIndex].Cells[6].Controls[0]).Text.Trim()); 
        cmd.Parameters.Add("@ThesisTitle", SqlDbType.NVarChar).Value = ((TextBox)GridView1.Rows[e.RowIndex].Cells[7].Controls[0]).Text; 
        cmd.Parameters.Add("@Describtion", SqlDbType.NVarChar).Value = ((TextBox)GridView1.Rows[e.RowIndex].Cells[8].Controls[0]).Text; 
        cmd.Parameters.Add("@HowzeEducationId", SqlDbType.Int).Value = GlobalVariables.HowzeEducationId; 
 
        cmd.ExecuteNonQuery(); 
 
    }