Я не хочу вводить только пробелы в текстовое поле в C#, но charector's with spaces ok. Вот мой код с ошибками.

private void btnsave_Click(object sender, EventArgs e)
       {
           if(comboslm.Text == "")
           {

               MessageBox.Show("Please Select Salesman Name");

               comboslm.Focus();
           }
          else if(slmname.Text=="" || slmname.Text==!char.IsWhiteSpace(e.KeyChar)) (Here only redline it is showing.So unable to render also)
           {

               MessageBox.Show("Empty Salesman Name Not Accepted");
               slmname.Focus();

           }
           else if (combosmancode.Text == "")
           {
               MessageBox.Show("Select Record Key Number");
               combosmancode.Focus();
           }
           else
           {
               SqlConnection con = new SqlConnection(@"Data Source=M2\SQL2016;Initial Catalog=inventoryDB;Integrated Security=True");
               con.Open();
               SqlCommand cmd = new SqlCommand("UPDATE smanDB SET smaname=@label2 WHERE smancode=@label4", con);
               cmd.Parameters.Add("@label2", slmname.Text);
               cmd.Parameters.Add("@label4", combosmancode.GetItemText(combosmancode.SelectedItem));
               cmd.ExecuteNonQuery();
               con.Close();
               MessageBox.Show("Updated Successfully");
              /* combosmancode.SelectedIndex = -1;
               comboslm.SelectedIndex = -1;
               slmname.Text = "";
               comboslm.Focus();*/
               con = new SqlConnection(@"Data Source=M2\SQL2016;Initial Catalog=inventoryDB;Integrated Security=True");
               con.Open();
               string query = "SELECT smaname FROM smanDB";
               string que = "SELECT smancode FROM smanDB";
               SqlDataAdapter da = new SqlDataAdapter(query, con);
               SqlDataAdapter sda = new SqlDataAdapter(que, con);
               DataSet ds = new DataSet();
               DataSet sds = new DataSet();
               da.Fill(ds, "smanDB");
               sda.Fill(sds, "smanDB");
               comboslm.DisplayMember = "smaname";
               comboslm.ValueMember = "smaname";
               comboslm.DataSource = ds.Tables["smanDB"];

               combosmancode.DisplayMember = "smancode";
               combosmancode.ValueMember = "smancode";
               combosmancode.DataSource = sds.Tables["smanDB"];

               combosmancode.SelectedIndex = -1;
               comboslm.SelectedIndex = -1;
               slmname.Text = "";
               con.Close();